
<PAGE>   1
                                                               EXHIBIT 99(a)(6)
        
 
 
            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9
 
     GUIDELINES FOR DETERMINING THE PROPER IDENTIFICATION NUMBER TO GIVE THE
PAYER -- Social Security Numbers have nine digits separated by two hyphens:
i.e., 000-00-0000. Employer Identification Numbers have nine digits separated by
only one hyphen: i.e., 00-0000000. The table below will help determine the type
of number to give the payer.
==============================================================
<TABLE>
<CAPTION>
                                      GIVE THE 
                                      SOCIAL SECURITY
     FOR THIS TYPE OF ACCOUNT:        NUMBER OF --
--------------------------------------------------------------
<S>  <C>                              <C>
 1.  An individual's account          The individual
 2.  Two or more individuals (joint   The actual owner of the
     account)                         account or, if combined
                                      funds, any one of the
                                      individuals(1)
 3.  Husband and wife (joint          The actual owner of the
     account)                         account or, if joint
                                      funds, either person(1)
 4.  Custodian account of a minor     The minor(2)
     (Uniform Gift to Minors Act)
 5.  Adult and minor (joint account)  The adult or, if the
                                      minor is the only
                                      contributor, the
                                      minor(1)
 6.  Account in the name of guardian  The ward, minor, or
     or committee for a designated    incompetent person(3)
     ward, minor, or incompetent
     person
 7.  a. The usual revocable savings   The grantor-trustee(1)
        trust account (grantor is
        also trustee)                 
     b. So-called trust account that  The actual owner(1)
        is not a legal or valid
        trust under State law
 8.  Sole proprietorship account      The owner(4)

</TABLE>

==============================================================
<TABLE>
<CAPTION>
                                      GIVE THE EMPLOYER
                                      IDENTIFICATION
     FOR THIS TYPE OF ACCOUNT:        NUMBER OF --
--------------------------------------------------------------
<S>  <C>                              <C>
 9.  A valid trust, estate, or        The legal entity (Do not
     pension trust                    furnish the identifying
                                      number of the personal
                                      representative or
                                      trustee unless the legal
                                      entity itself is not
                                      designated in the
                                      account title.)(5)
10.  Corporate account                The corporation
11.  Religious, charitable, or        The organization
     educational organization
     account
12.  Partnership account held in the  The partnership
     name of the business
13.  Association, club, or other      The organization
     tax-exempt organization
14.  A broker or registered nominee   The broker or nominee
15.  Account with the Department of   The public entity
     Agriculture in the name of a
     public entity (such as a State
     or local government, school
     district, or prison) that
     receives agricultural program
     payments
</TABLE>
================================================================================
 
(1) List first and circle the name of the person whose number you furnish.
(2) Circle the minor's name and furnish the minor's social security number.
(3) Circle the ward's, minor's or incompetent person's name and furnish such
     person's social security number.
(4) You must show your individual name, but you may also enter your business or
    "doing business" name. You may use either your Social Security Number or
    Employer Identification Number.
(5) List first and circle the name of the legal trust, estate, or pension trust.
NOTE: If no name is circled when there is more than one name, the number will be
      considered to be that of the first name listed.
<PAGE>   2
 
            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER OF SUBSTITUTE FORM W-9
 
                                     PAGE 2
 
OBTAINING A NUMBER
 
If you don't have a taxpayer identification number or you don't know your
number, obtain Form SS-5, Application for a Social Security Number Card, or Form
SS-4, Application for Employer Identification Number, at the local office of the
Social Security Administration or the Internal Revenue Service (the "IRS") and
apply for a number.
 
PAYEES EXEMPT FROM BACKUP WITHHOLDING
 
Payees specifically exempted from backup withholding on ALL payments include the
following:
 
- A corporation.
 
- A financial institution.
 
- An organization exempt from tax under section 501(a), or an individual
  retirement plan or a custodial account under Section 403(b)(7).
 
- The United States or any agency or instrumentality thereof.
 
- A State, the District of Columbia, a possession of the United States, or any
  subdivision or instrumentality thereof.
 
- A foreign government, a political subdivision of a foreign government, or any
  agency or instrumentality thereof.
 
- An international organization or any agency, or instrumentality thereof.
 
- A registered dealer in securities or commodities registered in the U.S. or a
  possession of the U.S.
 
- A real estate investment trust.
 
- A common trust fund operated by a bank under section 584(a).
 
- An exempt charitable remainder trust, or a non-exempt trust described in
  section 4947(a)(1).
 
- An entity registered at all times under the Investment Company Act of 1940.
 
- A foreign central bank of issue.
 
Payments of dividends and patronage dividends not generally subject to backup
withholding include the following:
 
- Payments to nonresident aliens subject to withholding under section 1441.

- Payments to partnerships not engaged in a trade or business in the U.S. and
  which have at least one nonresident partner.
 
- Payments of patronage dividends where the amount received is not paid in
  money.
 
- Payments made by certain foreign organizations.
 
- Payments made to a nominee.
 
Payments of interest not generally subject to backup withholding include the
following:
 
- Payments of interest on obligations issued by individuals. Note: You may be
  subject to backup withholding if this interest is $600 or more and is paid in
  the course of the payer's trade or business and you have not provided your
  correct taxpayer identification number to the payer.
 
- Payments of tax-exempt interest (including exempt-interest dividends under
  section 852).
 
- Payments described in section 6049(b)(5) to non-resident aliens.
 
- Payments on tax-free covenant bonds under section 1451.
 
- Payments made by certain foreign organizations.
 
- Payments made to a nominee.
 
Exempt payees described above should file Form W-9 to avoid possible erroneous
backup withholding. FILE THIS FORM WITH THE PAYER, FURNISH YOUR TAXPAYER
IDENTIFICATION NUMBER, CHECK "EXEMPT" IN PART II OF THE FORM, SIGN AND DATE THE
FORM AND RETURN IT TO THE PAYER.
 
Certain payments other than interest, dividends, and patronage dividends, that
are not subject to information reporting are also not subject to backup
withholding. For details, see the regulations under sections 6041, 6041A(a),
6045, and 6050A.
 
PRIVACY ACT NOTICE. -- Section 6109 requires most recipients of dividend,
interest, or other payments to give taxpayer identification numbers to payers
who must report the payments to IRS. IRS uses the numbers for identification
purposes. Payers must be given the numbers whether or not recipients are
required to file tax returns. Beginning January 1, 1993, payers must generally
withhold 31% of taxable interest, dividend, and certain other payments to a
payee who does not furnish a taxpayer identification number to a payer. Certain
penalties may also apply.
 
PENALTIES
 
(1) PENALTY FOR FAILURE TO FURNISH TAXPAYER IDENTIFICATION NUMBER. -- If you
fail to furnish your taxpayer identification number to a payer, you are subject
to a penalty of $50 for each such failure unless your failure is due to
reasonable cause and not to willful neglect.
 
(2) FAILURE TO REPORT CERTAIN DIVIDEND AND INTEREST PAYMENTS -- If you fail to
include any portion of an includible payment for interest, dividends, or
patronage dividends in gross income, such failure will be treated as being due
to negligence and will be subject to a penalty of 5% on any portion of an
under-payment attributable to that failure unless there is clear and convincing
evidence to the contrary.
 
(3) CIVIL PENALTY FOR FALSE INFORMATION WITH RESPECT TO WITHHOLDING. -- If you
make a false statement with no reasonable basis which results in no imposition
of backup withholding, you are subject to a penalty of $500.
 
(4) CRIMINAL PENALTY FOR FALSIFYING INFORMATION. -- Falsifying certifications or
affirmations may subject you to criminal penalties including fines and/or
imprisonment. FOR ADDITIONAL INFORMATION CONTACT YOUR TAX CONSULTANT OR THE
INTERNAL REVENUE SERVICE.
