<PAGE>   1
                                                                   EXHIBIT 10.15

                                 PROMISSORY NOTE
                                 (VARIABLE RATE)

<TABLE>
<CAPTION>
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   Principal      Loan Date      Maturity      Loan No.      Call       Collateral       Account       Officer      Initials
<S>               <C>            <C>           <C>           <C>        <C>              <C>           <C>          <C>
   $500,000        6/29/99        6/30/00                                  REL
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REFERENCES IN THE SHADED AREA ARE FOR LENDER'S USE ONLY AND DO NOT LIMIT THE APPLICABILITY OF THIS DOCUMENT TO ANY PARTICULAR
LOAN OR ITEM
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BORROWER:         TWENTY LINE INC.                          BANK: CALIFORNIA BANK & TRUST
                  3883 RUFFIN ROAD, SUITE A                       2141 PALOMAR AIRPORT ROAD, SUITE 125
                  SAN DIEGO, CALIFORNIA 92123                     CARLSBAD, CALIFORNIA 92009
                  ATTENTION: MR. TOM HIGGINSON                    ATTENTION: NORTH COUNTY CORPORATE BANKING
</TABLE>

1.       FUNDAMENTAL PROVISIONS. The following terms will be used as defined
         terms in this Note:

         DATE OF THIS NOTE:      June 29, 1999.

         BORROWER:               TWENTY LINE, INC., a Louisiana corporation.

         BANK:                   CALIFORNIA BANK & TRUST, a California banking
                                 corporation.

         PRINCIPAL AMOUNT:       Five Hundred Thousand Dollars ($500,000).

         INTEREST RATE:          One and 00/100 percentage point (1.00%) per
                                 annum above the Index Rate. The Interest Rate
                                 shall change from time to time as and when the
                                 Index Rate changes.

         DEFAULT RATE:           Five percent (5%) per annum above the Interest
                                 Rate. The Default Rate shall change from time
                                 to time as and when the Index Rate changes.

         INDEX RATE:             The "California Bank & Trust Prime Rate" as
                                 announced from time to time by Bank. In the
                                 event Bank should cease to announce a
                                 California Bank & Trust Prime Rate, the Index
                                 shall be the "Prime Rate" as published from
                                 time to time in the Western edition of the Wall
                                 Street Journal, and if a range of rates or more
                                 than one such rate is published, the Index Rate
                                 shall be the highest rate so published.

         MATURITY DATE:          June 30, 2000.

         PROPERTY:               The real property located in Shreveport,
                                 Louisiana, more particularly described in the
                                 Loan A Agreement.

2.       PROMISE TO PAY. For good and valuable consideration, Borrower promises
         to pay to Bank, or order, the Principal Amount, or so much of the
         Principal Amount as may be advanced under this Note, with interest from
         the date of each such advance at the Interest Rate, or at the Default
         Rate as hereinafter provided, until paid in full in accordance with the
         terms contained herein.

3.       LOAN AGREEMENT. This Note evidences a loan from Bank to Borrower
         pursuant to a Construction Loan Agreement dated the same as this Note
         ("Loan Agreement"). Terms defined in the Loan Agreement and not
         otherwise defined herein are used herein with the meanings defined for
         those terms in the Loan Agreement. This is the Note referred to in the
         Loan Agreement, and any holder hereof is entitled to all of the rights,
         remedies, benefits and privileges provided for in the Loan Agreement as
         originally executed or as it may from time to time be supplemented,
         modified or amended. The Loan Agreement, among other things, contains
         provisions for acceleration of the maturity hereof upon the happening
         of certain stated events upon the terms and conditions therein
         specified.


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4.       PAYMENT. Borrower shall pay regular monthly payments of accrued unpaid
         interest beginning August 1, 1999, and all subsequent interest payments
         are due on the first day of each month after that through the Maturity
         Date, on or before which date Borrower shall pay the loan evidenced by
         this Note ("Loan") on which date all outstanding principal plus accrued
         unpaid interest on the Loan shall be due and payable in full. To the
         extent available and not previously disbursed, the portion of the Cost
         Breakdown designated as the Interest Reserve Amount shall be disbursed,
         from time to time, directly to Bank in payment of interest which
         accrues and becomes due under the Note; and Bank is hereby authorized
         to charge the Loan and Borrower's Funds Account directly for such
         interest payments as they become due. Interest on this Note is computed
         on a 365/360 simple interest basis, i.e., by applying the ratio of the
         annual interest rate over a year of 360 days, multiplied by the
         outstanding principal balance, multiplied by the actual number of days
         the principal balance is outstanding. Unless otherwise agreed or
         required by applicable law, payments will be applied first to unpaid
         collection costs and late charges, then to accrued unpaid interest, and
         any remaining amount to principal. Principal may be prepaid at any
         time, in whole or in part, without penalty.

5.       PLACE AND MANNER OF PAYMENT. All payments shall be made at the address
         for Bank set forth above, or at such other place as the holder of this
         Note may from time to time designate. All payments shall be made in
         lawful money of the United States. Checks will constitute payment only
         when collected.

6.       STRAIGHT LINE OF CREDIT. The Loan is a non-revolving, straight line of
         credit. Once the total Principal Amount has been advanced, Borrower is
         not entitled to further loan disbursements. Borrower agrees to be
         liable for all sums either: (i) advanced in accordance with the
         instructions of an authorized person, or (ii) credited to any of
         Borrower's accounts with Bank. The unpaid principal balance owing on
         this Note at any time may be evidenced by endorsements on this Note or
         by Bank's internal records, including daily computer print-outs.

7.       LATE CHARGES. If Borrower fails to make any payment of principal or
         interest within ten (10) days after the date on which the same is due
         and payable, a late charge constituting damages shall be immediately
         due and payable. Borrower recognizes that a default in making the
         payments herein agreed to be made as and when due will result in Bank's
         incurring additional expenses in servicing this Note, in loss to Bank
         of the use of the money due, and in frustration to Bank in meeting its
         other commitments, but that it is extremely difficult and impractical
         to ascertain the extent of such damages. Accordingly, Borrower agrees
         that the late charge for any such payment described above that is not
         paid within the period specified above after the date when due shall be
         an amount equal to five cents ($.05) for each dollar ($1.00) of each
         payment which becomes so delinquent, as a reasonable estimate of the
         damages to Bank, which sum shall be immediately due and payable.

8.       DEFAULT INTEREST RATE. Commencing on the earlier of the maturity of
         this Note or the occurrence of an Event of Default followed by the
         acceleration of this Note and the lapse of such time (if any) as may
         then be required by law during which Bank must allow Borrower to
         reinstate the obligation evidenced hereby as if no acceleration had
         occurred, and continuing thereafter until this Note has been paid in
         full, all amounts due and owing under this Note shall bear interest at
         the Default Rate. The provisions of this paragraph shall not limit
         Bank's right to compel prompt performance hereunder.

9.       ACCELERATION ON TRANSFER. Borrower acknowledges that (i) the financial
         stability and managerial and operational ability of Borrower were and
         are a substantial and material consideration to Bank, and in reliance
         thereon, Bank agreed to make the Loan to Borrower evidenced by this
         Note and the Loan Agreement, and (ii) the transfer of possession of the
         Property or any portion thereof or interest therein, or a change in the
         person or entity operating and managing either the Property or
         Borrower, may significantly and materially alter or reduce Bank's
         security for this Note. Accordingly, as a material inducement to Bank
         to enter into the transaction contemplated by the Loan Agreement,
         Borrower agrees that it shall not transfer the Property or any portion
         thereof or interest therein without the prior written consent of Bank,
         except as provided under the Loan Agreement. As used herein, "transfer"
         shall mean any event described in the paragraph of the Loan Agreement
         captioned "Conveyance, Lease or Encumbrance" or any change in Borrower
         described in the paragraph thereof captioned "Change in Borrower". In
         the event of any such transfer, Bank shall have the right to declare
         the entire principal balance, plus interest and other charges due
         hereunder or under the Loan Agreement, immediately due and payable in
         full.

10.      EVENT OF DEFAULT. At the option of Bank, it shall be an "Event of
         Default" hereunder if (i) Borrower fails to pay when due any sum
         payable under this Note, or (ii) Borrower fails to perform any
         obligation or commits a breach of any agreement


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         set forth in this Note, if such failure is not cured within five (5)
         days after written notice from Bank, or (iii) any default or Event of
         Default occurs under the Deed of Trust or the Loan Agreement.

11.      ACCELERATION ON DEFAULT. Upon the occurrence of an Event of Default, at
         the option of Bank, the entire sum of principal, interest and all other
         charges due under this Note shall become immediately due and payable.

12.      ATTORNEYS' FEES. If Bank refers this Note to an attorney to enforce,
         construe or defend any provision hereof, or as a consequence of any
         Event of Default hereunder, with or without the filing of any legal
         action or proceeding, Borrower shall pay to Bank upon demand the amount
         of all attorneys' fees, costs and other expenses incurred by Bank in
         connection therewith, together with interest thereon from the date of
         demand at the rate applicable to the principal balance of this Note.

13.      NO WAIVER. No delay or omission of Bank in exercising any right or
         power arising in connection with any Event of Default shall be
         construed as a waiver thereof or as an acquiescence therein, nor shall
         any single or partial exercise thereof preclude any further exercise
         thereof. Bank may, at its option, waive any of the conditions herein
         and no such waiver shall be deemed to be a waiver of Bank's rights
         hereunder, but rather shall be deemed to have been pursuant to this
         Note and not in modification thereof. No waiver of any Event of Default
         shall be construed to be a waiver of or acquiescence in or consent to
         any preceding or subsequent Event of Default.

14.      WAIVER OF NOTICES. Borrower, all endorsers, all guarantors and all
         persons liable or to become liable on this Note, waive presentment,
         protest, demand, notice of protest, dishonor or non-payment of this
         Note, and any and all other notices or matters of a like nature,
         consent to any and all renewals and extensions of the time of payment
         hereto, and agree further that at any time and from time to time
         without notice, the terms of payment hereof may be modified, or the
         security described in the Loan Agreement at any time securing this Note
         may be released in whole or in part, or increased, changed or exchanged
         by agreement between the holder hereof and any owner of the Property or
         other collateral affected thereby, without in any way affecting the
         liability of any party to this Note, any endorser, any guarantor or any
         person liable or to become liable with respect to any indebtedness
         evidenced hereby.

15.      MISCELLANEOUS PROVISIONS. No provision of this Note may be amended,
         modified, supplemented, changed, waived, discharged or terminated
         unless Bank consents thereto in writing. In case any one or more of the
         provisions contained in this Note should be held to be invalid, illegal
         or unenforceable in any respect, the validity, legality and
         enforceability of the remaining provisions contained herein shall not
         in any way be affected or impaired thereby. This Note shall be binding
         upon and inure to the benefit of Borrower, Bank and their respective
         successors and assigns. Time is of the essence of this Note and the
         performance of each of the covenants and agreements contained herein.
         If Borrower consists of more than one person or entity, the obligations
         of Borrower shall be the joint and several obligations of all such
         persons or entities, and any married person who executes this Note
         agrees that recourse may be had against his or her separate property
         for satisfaction of his or her obligations hereunder.

16.      CHOICE OF LAW. This Note shall be governed by and construed in
         accordance with the laws of the State of California, including its
         conflict of laws rules, notwithstanding that the real property security
         for the Loan is located in the State of Louisiana, whose laws will
         govern only the lien and enforcement of the Deed of Trust.

IN WITNESS WHEREOF, Borrower has executed this Note as of the Date of this Note.

BORROWER:                             TWENTY LINE, INC., a Louisiana corporation


                                      By: /s/
                                          --------------------------------------
                                      Its:
                                          --------------------------------------



                                      By: /s/
                                          --------------------------------------
                                      Its:
                                          --------------------------------------


ABC
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                                    GUARANTY

         1. FOR VALUE RECEIVED, including the extension of the maturity date
extended to TWENTY LINE, INC., a Louisiana corporation ("Borrower"), which
maturity date, in the absence of this Guaranty would not have been extended, the
undersigned BRENTO CORP., an Arizona corporation ("Guarantor"), hereby
unconditionally and irrevocably guarantees to CALIFORNIA BANK & TRUST, a
California banking corporation ("Bank"):

                  (a) To pay, when due, whether at maturity, by acceleration or
otherwise, or as the same may be renewed, modified or extended from time to
time, whether for principal, interest or otherwise, all indebtedness represented
by that certain Promissory Note dated July 29, 1999, signed, made and delivered
by Borrower to the order of Bank in the principal amount of Five Hundred
Thousand Dollars ($500,000) ("Note");

                  (b) Strict performance of Borrower's obligations under that
certain Collateral Mortgage, dated the same as the Note, which was recorded in
the Official Records of Caddo Parish, Louisiana on August 4, 1999 ("Collateral
Mortgage");

                  (c) Strict performance of Borrower's obligations under that
certain Construction Loan Agreement between Borrower and Bank dated the same as
the Note ("Loan Agreement"), including without limitation Borrower's obligations
to construct improvements as described therein; and

                  (d) Strict performance of Borrower's obligations under that
certain Unsecured Environmental Indemnity made by Borrower in favor of Bank
dated the same as the Note.

The Note, Collateral Mortgage, Loan Agreement and Unsecured Indemnity Agreement
shall be referred to collectively as the "Loan Documents", certain of which were
amended as of June 30, 2000 by that certain Loan Modification Agreement of that
date between Bank and Borrower.

         2. The obligations of Guarantor under this Guaranty are independent of
the obligations of Borrower. The liability of Guarantor under this Guaranty
shall be (i) joint and several with the liability of each and every other person
guaranteeing the obligations of Borrower under the Loan Documents ("other
guarantor"); and (ii) continuing and shall only be terminated by full
performance by Borrower pursuant to all of the terms of all of the Loan
Documents. Guarantor expressly and specifically agrees that upon default by
Borrower, a separate action or actions may be brought and prosecuted against
Guarantor, whether or not action is brought against Borrower or any other
guarantor (or both), and whether or not Borrower or any other guarantor (or
both) is joined in any action against Guarantor on this Guaranty.

         3. Guarantor authorizes Bank, without notice or demand and without
affecting Guarantor's liability under this Guaranty, from time to time, to: (i)
change or extend the time or manner of payment of the Note; (ii) change any of
the terms, covenants, conditions or provisions of the Collateral Mortgage or any
other Loan Document; (iii) transfer, assign or negotiate the Note and transfer
and assign the Collateral Mortgage and the other Loan Documents; (iv) take and
hold additional security for the payment of the Note or the performance of the
Collateral Mortgage or other Loan Document(s); (v) release all or part of the
collateral from the Collateral Mortgage; (vi) apply the property conveyed by the
Collateral Mortgage and direct the order or manner of sale thereof as Bank in
its sole, absolute and unfettered discretion may determine; (vii) proceed
against Borrower, any other guarantor or Guarantor (or any combination of them)
on the Note without first foreclosing under the Collateral Mortgage; (viii)
accept a conveyance of all or part of the property conveyed by the Collateral
Mortgage in partial satisfaction of the indebtedness due under the Note and
proceed against Borrower, any other guarantor or Guarantor (or any combination
of them) for the balance then due thereunder. No indulgence, forbearance or
extensions of time of payment or performance permitted or granted to Borrower by
Bank shall in any way release Guarantor from liability or diminish Guarantor's
obligations under this


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Guaranty. Guarantor waives all rights and defenses arising out of an election of
remedies by the creditor, even though that election of remedies, such as a
non-judicial foreclosure with respect to security for a guaranteed obligation,
has destroyed Guarantor's rights of subrogation and reimbursement against the
principal by operation of `580d of the CODE OF CIVIL PROCEDURE or otherwise.
Upon default by Borrower, Guarantor hereby waives:

                  (a) Presentment, demand, protest, notice of protest, notice of
dishonor, notice of nonpayment and notice of acceptance of this Guaranty.

                  (b) The right, if any, to the benefit of, or to direct the
application of any security held by Bank, including the property described in
the Collateral Mortgage; and, until all the indebtedness, payment of which is
hereby guaranteed, has been paid in full, all rights of subrogation, any right
to enforce any remedy which Bank now has or hereafter may have against Borrower
or any other guarantor, and any right to participate in any security now or
hereafter held by Bank.

                  (c) The right to require Bank to proceed against Borrower or
any other guarantor (or any combination of them) or to proceed against any
security now or hereafter held by Bank or to pursue any other remedy in Bank's
power.

                  (d) The benefits, if Guarantor is entitled to any benefits, of
any and all fair-market value and anti-deficiency statutes or single-action
legislation, including, but not limited to, ` ` 580a, 580d or 726 of the
California CODE OF CIVIL PROCEDURE.

                  (e) Any and all rights, claims and defenses arising out of or
based upon any exercise or election of remedies by Bank which affects or results
in the absence, impairment, destruction or loss of any right of reimbursement,
contribution, indemnification, subrogation or other right or remedy Guarantor
may have against Borrower, any other guarantor or any security to recover or
seek reimbursement for any amount paid by Guarantor under this Guaranty.
Guarantor acknowledges, in this regard, that the exercise by Bank of certain
rights and remedies set forth in the Loan Documents may adversely affect or even
eliminate Guarantors' subrogation rights against Borrower, if any, and that as a
result Guarantor may succeed to a partially or totally unreimbursable liability
hereunder. Nevertheless, Guarantor expressly authorizes Bank to exercise in its
sole discretion any and all rights and remedies available to Bank under the Loan
Documents, without regard to their affect on Guarantor's subrogation or other
rights against Borrower. The foregoing acknowledgments and waivers are intended
to include, but not be limited to, a full, complete and knowing waiver in
advance of any and all rights, claims and defenses based on (i) Union Bank v.
Gradsky, 265 Cal.App.2d 40 (1968); (ii) Bank's election to conduct a private
non-judicial foreclosure sale by exercising the power of sale under the
Collateral Mortgage (notwithstanding that Bank's doing so may by operation of'
580d of the California CIVIL CODE destroy any subrogation rights Guarantor might
otherwise have had); (iii) any disability or other defense of Borrower or any
other guarantor; (iv) the cessation, from any cause, of the liability of
Borrower or any other guarantor; and (v) ` ` 2809, 2810, 2819, 2845, 2848, 2849,
2850 and 2855 of the California CIVIL CODE.

                  (f) Any and all rights, claims and defenses arising out of or
based upon `580a of the California CODE OF CIVIL PROCEDURE, including the right
to a fair market value hearing, the right to limit the size of any deficiency
judgment, and any right of Guarantor to limit any recovery by Bank hereunder to
the amount by which the total of the guaranteed indebtedness exceeds the fair
market value of the real property encumbered by the Collateral Mortgage at the
time of foreclosure thereof. Guarantor acknowledges, in this regard, that if
Bank should elect to foreclose non-judicially and then bring an action under
this Guaranty for any deficiency, Guarantor would by virtue of the foregoing
waiver have relinquished any right to the protections of a fair market value
hearing under `580a of the California CODE OF CIVIL PROCEDURE, and would as a
result be liable to Bank for the full amount of any deficiency between the
guaranteed indebtedness and the foreclosure sale proceeds, even if the
fair-market value of the foreclosed property was more than the foreclosure sale
proceeds.


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                  (g) To the extent permitted by applicable law, the benefit of
or right to assert any statute of limitations affecting Guarantor's liability
under this Guaranty or the enforcement of this Guaranty.

                  (h) To the extent applicable and permitted by law, Guarantor
waives all rights and remedies that Guarantor may have been able to assert by
reason of the laws of the State of Louisiana pertaining to the rights and
remedies of sureties including, without limitation: (i) any right Guarantor
otherwise might have to require Bank to make any demand upon, proceed against,
or exhaust any security given by, Borrower and/or any other person or entity
before seeking enforcement of this Guaranty, or to pursue any legal, equitable
or statutory remedy otherwise available to Bank in any particular manner or
order.

         Any part payment by Borrower or any other guarantor or any other
circumstances which operate to toll any statute of limitations as to Borrower or
any other guarantor (or both) shall also operate to toll the statute of
limitations as to Guarantor.

         4. Any indebtedness of Borrower now or hereafter held by Guarantor is
hereby subordinated to the indebtedness of Borrower to Bank; and any
indebtedness of Borrower to Guarantor, if Bank so requests, shall be collected,
enforced and received by Guarantor as trustee for Bank on account of the
indebtedness of Borrower to Bank without affecting the liability of Guarantor
under this Guaranty. Notwithstanding the foregoing, prior to an event of default
under the Loan Documents, and following the cure of all event of default
thereunder, Borrower may pay, and Guarantor may accept, any payments on the
account of any such indebtedness.

         5. With respect to any claim arising out of or related to this
Guaranty, Guarantor waives all rights of subrogation, reimbursement, indemnity
and contribution against Borrower, all rights to enforce any remedy Lender may
have against Borrower, and all rights to participate in any security held by
Lender for the guaranteed obligations, including any such right or any other
right set forth in either `2848 or `2849 of the California CIVIL CODE, as well
as any defense based upon the impairment of any subrogation, reimbursement,
indemnity or contribution rights, or of any of the other foregoing rights, that
Guarantor might have absent the waivers in Paragraph 3 above. Guarantor agrees
(i) not to seek to enforce or to obtain any such right, or to accept any payment
from any other person, in violation of the foregoing waiver; and (ii) that any
agreement or other understanding at any time entered into with any person
granting any such right to Guarantor shall be null and void.

         6. With respect to any claim arising out of or related to this
Guaranty, Guarantor irrevocably waives, to the fullest extent possible, all
rights, actions, causes of action and claims of every kind and nature against
Borrower, including, but not limited to, all rights to be or become a creditor
of Borrower. Guarantor releases Borrower from all claims that may now or in the
future exist or arise in favor of Guarantor based on any theory of law or equity
or any statutory or common law principle, including, but not limited to,
theories or laws based upon principles of indemnity, reimbursement,
contribution, subrogation and subordination. Guarantor further irrevocably
waives all other rights of recourse against Borrower that may otherwise exist by
virtue of this Guaranty.

         7. Paragraphs 5 and 6 hereof shall not constitute a waiver or a release
of Borrower as to any claim other than a claim related to or arising out of this
Guaranty and the guaranteed indebtedness to which this Guaranty relates.

         8. Although Borrower is an entity, it is not necessary for Bank to
inquire into the powers of Borrower or of its officers, directors, shareholders,
partners, members and/or managers, as applicable, or their respective agents
acting or purporting to act on behalf of Borrower, and any indebtedness made or
created in reliance upon the professed exercise of such powers shall be
guaranteed under this Guaranty.

         9. Guarantor agrees to pay reasonable attorneys' fees and all other
costs and expenses which may be incurred by Bank in the enforcement of this
Guaranty.


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         10. This Guaranty shall bind the successors and assigns of Guarantor
and inure to the benefit of the successors and assigns of Bank.

         11. This Guaranty shall follow the Note and Collateral Mortgage, and if
the Note and Collateral Mortgage are sold, transferred, assigned or conveyed by
Bank, then this Guaranty may be likewise sold, transferred, assigned or conveyed
by Bank to the holder of the Note and Collateral Mortgage, and in such event,
the holder of this Guaranty may enforce this Guaranty just as if said holder had
been originally named as "Bank" under this Guaranty.

         Signed and made at San Diego County, California, as of July 1, 2000.

                                        BRENTO CORP., an Arizona corporation



                                        By /s/ David A. Altomare
                                          ----------------------------------
                                        Its: CEO
                                            --------------------------------


                                        By
                                          ----------------------------------
                                        Its
                                           ---------------------------------


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