<PAGE>

                                                                    Exhibit 4.30

                          CAPITAL SECURITY CERTIFICATE

     THIS CAPITAL SECURITY IS A GLOBAL CAPITAL SECURITY WITHIN THE MEANING OF
THE DECLARATION HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE
DEPOSITORY TRUST COMPANY (THE "CLEARING AGENCY") OR A NOMINEE OF THE CLEARING
AGENCY.  THIS CAPITAL SECURITY IS EXCHANGEABLE FOR CAPITAL SECURITIES REGISTERED
IN THE NAME OF A PERSON OTHER THAN THE CLEARING AGENCY OR ITS NOMINEE ONLY IN
THE LIMITED CIRCUMSTANCES DESCRIBED IN THE DECLARATION AND NO TRANSFER OF THIS
CAPITAL SECURITY (OTHER THAN A TRANSFER OF THIS CAPITAL SECURITY AS A WHOLE BY
THE CLEARING AGENCY TO A NOMINEE OF THE CLEARING AGENCY OR BY A NOMINEE OF THE
CLEARING AGENCY TO THE CLEARING AGENCY OR ANOTHER NOMINEE OF THE CLEARING
AGENCY) MAY BE REGISTERED EXCEPT IN LIMITED CIRCUMSTANCES.

     UNLESS THIS CAPITAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE
OF THE CLEARING AGENCY TO THE TRUST OR ITS AGENT FOR REGISTRATION OF TRANSFER,
EXCHANGE OR PAYMENT, AND ANY CAPITAL SECURITY ISSUED IS REGISTERED IN THE NAME
OF CEDE & CO.  OR SUCH OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE
OF THE CLEARING AGENCY AND ANY PAYMENT HEREON IS MADE TO CEDE & CO., ANY
TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON
IS WRONGFUL SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
HEREIN.

     THE CAPITAL SECURITIES WILL BE ISSUED AND MAY BE TRANSFERRED ONLY IN BLOCKS
HAVING A LIQUIDATION AMOUNT OF NOT LESS THAN $100,000 (100 CAPITAL SECURITIES)
AND MULTIPLES OF $1,000 IN EXCESS THEREOF.  ANY ATTEMPTED TRANSFER OF CAPITAL
SECURITIES IN A BLOCK HAVING A LIQUIDATION AMOUNT OF LESS THAN $100,000 (100
CAPITAL SECURITIES) SHALL BE DEEMED TO BE VOID AND OF NO LEGAL EFFECT
WHATSOEVER.  ANY SUCH PURPORTED TRANSFEREE SHALL BE DEEMED NOT TO BE THE HOLDER
OF SUCH CAPITAL SECURITIES FOR ANY PURPOSE, INCLUDING, BUT NOT LIMITED TO, THE
RECEIPT OF DISTRIBUTIONS ON SUCH CAPITAL SECURITIES, AND SUCH PURPORTED
TRANSFEREE SHALL BE DEEMED TO HAVE NO INTEREST WHATSOEVER IN SUCH CAPITAL
SECURITIES.
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Certificate Number: S-001                Aggregate Liquidation Amount:
CUSIP Number:  361467-AC7                $41,000,000

                   Certificate Evidencing Capital Securities

                                      of

                                GBB Capital IV

                      10.75% Capital Securities, Series B
               (liquidation amount $1,000 per Capital Security)

  GBB Capital IV, a statutory business trust created under the laws of the State
of Delaware (the "Trust"), hereby certifies that Cede & Co. (the "Holder") is
the registered owner of $41,000,000 in aggregate liquidation amount of Capital
Securities of the Trust representing undivided preferred beneficial interests in
the assets of the Trust designated the 10.75% Capital Securities, Series A
(liquidation amount $1,000 per Capital Security) (the "Capital Securities").
The Capital Securities are transferable on the books and records of the Trust,
in person or by a duly authorized attorney, upon surrender of this certificate
duly endorsed and in proper form for transfer.  The designation, rights,
privileges, restrictions, preferences and other terms and provisions of the
Capital Securities represented hereby are issued and shall in all respects be
subject to the provisions of the Amended and Restated Declaration of Trust,
dated as of May 19, 2000, as the same may be amended from time to time (the
"Declaration"), including the designation of the terms of the Capital Securities
as set forth in Annex I to the Declaration.  Capitalized terms used but not
defined herein shall have the meaning given them in the Declaration.  The
Sponsor will provide a copy of the Declaration, the Capital Securities Guarantee
and the Indenture (including any supplemental indenture) to a Holder without
charge upon written request to the Trust at its principal place of business.

     Upon receipt of this Certificate, the Holder is bound by the Declaration
and is entitled to the benefits thereunder and to the benefits of the Capital
Securities Guarantee to the extent provided therein.

     By acceptance hereof, the Holder agrees, for United States federal income
tax purposes, to treat the Debentures as indebtedness and the Capital Securities
as evidence of indirect beneficial ownership in the Debentures.
<PAGE>

          IN WITNESS WHEREOF, the Trust has executed this certificate this 20th
day of November, 2000.

                                GBB CAPITAL IV

                                By: /s/ Shawn E. Saunders
                                    ---------------------
                                   Shawn E. Saunders
                                   Administrative Trustee

                                       3
<PAGE>

               PROPERTY TRUSTEE'S CERTIFICATE OF AUTHENTICATION

This is one of the 10.75% Capital Securities, Series B of GBB Capital IV
referred to in the within-mentioned Declaration.

Dated:  November 20, 2000

                              WILMINGTON TRUST COMPANY,
                              not in its individual capacity but solely
                              as Property Trustee


                              By: /s/ Bruce L. Bisson
                                  -------------------
                                 Authorized Signatory

                                       4
<PAGE>

     Distributions on each Capital Security will be payable at a fixed rate per
annum of 10.75% (the "Coupon Rate") of the liquidation amount of $1,000 per
Capital Security, such rate being the rate of interest payable on the Debentures
to be held by the Property Trustee.  Distributions in arrears for more than one
semi-annual period will bear interest thereon compounded semi-annually at the
Coupon Rate (to the extent permitted by applicable law).  Pursuant to the
Registration Rights Agreement and the Liquidated Damages Agreement, in certain
limited circumstances the Debenture Issuer will be required to pay Liquidated
Damages (as defined in the Registration Rights Agreement and the Liquidated
Damages Agreement) with respect to the Debentures.  The term "Distributions," as
used herein, includes such cash distributions and any and all such interest and
Liquidated Damages, if any, payable unless otherwise stated.  A Distribution is
payable only to the extent that payments are made in respect of the Debentures
held by the Property Trustee and to the extent the Property Trustee has funds
legally available therefor.

     Distributions on the Capital Securities will be cumulative, will accumulate
from the most recent date to which Distributions have been paid or, if no
Distributions have been paid, from May 19, 2000 and will be payable semi-
annually in arrears, on June 1st and December 1st of each year, commencing
December 1, 2000, except as otherwise described below.  Distributions will be
computed on the basis of a 360-day year of twelve 30-day months.  As long as no
Event of Default has occurred and is continuing under the Indenture, the
Debenture Issuer has the right under the Indenture to defer payments of interest
by extending the interest payment period at any time and from time to time on
the Debentures for a period not exceeding ten consecutive semi-annual calendar
periods, including the first such semi-annual period during such extension
period (each an "Extension Period"), provided that no Extension Period shall end
                                     -------- ----
on a date other than an Interest Payment Date for the Debentures or extend
beyond the Maturity Date of the Debentures.  As a consequence of such deferral,
Distributions (other than Liquidated Damages, if any) will also be deferred.
Notwithstanding such deferral, semi-annual Distributions will continue to
accumulate with interest thereon (to the extent permitted by applicable law, but
not at a rate exceeding the rate of interest then accruing on the Debentures) at
the Coupon Rate compounded semi-annually during any such Extension Period.
Prior to the termination of any Extension Period, the Debenture Issuer may
further defer payments of interest by further extending such Extension Period;
provided that such Extension Period, together with all such previous and further
-------- ----
extensions within such Extension Period, may not (i) exceed ten consecutive
semi-annual periods, including the first semi-annual period during such
Extension Period, (ii) end on a date other than an Interest Payment Date for the
Debentures or (iii) extend beyond the Maturity Date of the Debentures.  Payments
of accumulated Distributions will be payable to Holders as they appear on the
books and records of the Trust on the record date immediately preceding the end
of the Extension Period.  Upon the termination of any Extension Period and the
payment of all amounts then due, the Debenture Issuer may commence a new
Extension Period, subject to the above requirements.

     Subject to receipt by the Sponsor of any and all required regulatory
approvals and to certain other conditions set forth in the Declaration and the
Indenture, the Property Trustee may, at the direction of the Sponsor, at any
time dissolve the Trust and after satisfaction of liabilities to creditors of
the Trust as provided by applicable law, cause the Debentures to be distributed
to the Holders of the Securities in liquidation of the Trust or, simultaneously
with any redemption of the Debentures, cause a Like Amount of the Securities to
be redeemed by the Trust.

     The Capital Securities shall be redeemable as provided in the Declaration.

                                       5
<PAGE>

The following abbreviations, when used in the inscription on the face of this
Certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

TEN CON - as tenants in common
TEN ENT - as tenants in the entireties
JT TEN - as joint tenants with right of survival
UNIF GIFT MIN ACT - under Uniform Gift to Minors Act and not as tenants
Additional abbreviations may also be used though not in the above list.

                               _______________

                                  ASSIGNMENT

                               _______________

FOR VALUE RECEIVED, the undersigned hereby assigns and transfers this Capital
Security Certificate to:

________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
           (Assignee's social security or tax identification number)

________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
                      (Address and zip code of assignee)

and irrevocably appoints

________________________________________________________________________________
________________________________________________________________________________
__________________________________________________________________________ agent
to transfer this Capital Security Certificate on the books of the Trust.  The
agent may substitute another to act for him or her.

Date:__________________

Signature:________________________________________________________
(Sign exactly as your name appears on the other side of this Capital Security
Certificate)

Signature Guarantee:______________________________________________

___________________________
     Signature must be guaranteed by an "eligible guarantor institution" that is
     a bank, stockbroker, savings and loan association or credit union meeting
     the requirements of the Registrar, which requirements include membership or
     participation in the Securities Transfer Agents Medallion Program ("STAMP")
     or such other "signature guarantee program" as may be determined by the
     Registrar in addition to, or in substitution for, STAMP, all in accordance
     with the Securities Exchange Act of 1934, as amended.

                                       6
<PAGE>

In connection with any transfer of any of the Capital Securities evidenced by
this Certificate, the undersigned confirms that such Capital Securities are
being:

CHECK ONE BOX BELOW

          (1)  [_]   exchanged for the undersigned's own account without
                     transfer; or

          (2)  [_]   transferred pursuant to and in compliance with Rule 144A
                     under the Securities Act of 1933, as amended; or

          (3)  [_]   transferred to an institutional "accredited investor"
                     within the meaning of subparagraph (a)(1), (2), (3) or (7)
                     of Rule 501 under the Securities Act of 1933 that is
                     acquiring the Capital Securities for its own account, or
                     for the account of such an institutional "accredited
                     investor," for investment purposes and not with a view to,
                     or for offer or sale in connection with, any distribution
                     in violation of the Securities Act of 1933, as amended; or

          (4)  [_]   transferred pursuant to another available exemption from
                     the registration requirements of the Securities Act of
                     1933, as amended; or

          (5)  [_]   transferred pursuant to an effective registration
                     statement.

Unless one of the boxes is checked, the Registrar will refuse to register any of
the Capital Securities evidenced by this Certificate in the name of any Person
other than the Holder hereof; provided, however, that if box (3) or (4) is
                              --------  -------
checked, the Registrar may require, prior to registering any such transfer of
the Capital Securities, such legal opinions, certifications and other
information as the Trust has reasonably requested to confirm that such transfer
is being made pursuant to an exemption from, or in a transaction not subject to,
the registration requirements of the Securities Act of 1933, as amended, such as
the exemption provided by Rule 144 under such Act; provided, further, that (i)
                                                   --------  -------
if box (2) is checked, by acceptance of this Certificate, the transferee shall
be deemed to have certified that it is a "qualified institutional buyer" (as
defined in Rule 144A) ("QIB") acquiring the Capital Securities for its own
account or for the account of another QIB over which it exercises sole
investment discretion and that it is aware that the Holder is relying upon the
exemption from registration afforded by Rule 144A in respect of the Holder's
transfer of Capital Securities to it or (ii) if box (3) is checked, the
transferee must also provide to the Registrar a Transferee Letter of
Representation in the form attached to the Offering Memorandum of the Trust
dated May 16, 2000; provided, further, that after the date that a registration
                    --------  -------
statement has been filed and so long as such Registration Statement continues to
be effective, only then may the Registrar permit transfers for which box (5) has
been checked.


                                               _________________________________
                                                            Signature

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