<PAGE>

                                                                    EXHIBIT 10.8

                  AMENDMENT TO DEMAND LINE OF CREDIT AGREEMENT
                         AND DEMAND LINE OF CREDIT NOTE


THIS AMENDMENT, dated July ___, 2003, is to the Demand Line of Credit Agreement
between Zero Zone, Inc., ("Borrower") and U.S. Bank, N.A. ("Bank") dated August
30, 1999 (the "Credit Agreement") and the Demand Line of Credit Note executed by
Borrower in favor of Bank dated August 30, 1999 (the "Note").

WHEREAS, Borrower and Bank are entering into a Third Amendment to Direct Pay
Letter of Credit Application and Reimbursement Agreements (the "Third
Amendment") relating to the Reimbursement Agreements (as defined hereinafter);
and

WHEREAS, "Reimbursement Agreements" means the Direct Pay Letter of Credit
Application and Reimbursement Agreement between Bank and Borrower regarding the
$6,000,000 Zero Zone, Inc. Taxable Bonds, Series 1999 dated as of August 31,
1999, as amended by Amendment to Direct Pay Letter of Credit Application and
Reimbursement Agreements (the "First Amendment") dated as of January 31, 2002,
the Second Amendment to Direct Pay Letter of Credit Application and
Reimbursement Agreements (the "Second Amendment") dated February 5, 2003 and the
Third Amendment to Direct Pay Letter of Credit Application and Reimbursement
Agreement (the "Third Amendment") dated of even date with this Amendment (as
amended and as it may be amended from time to time, the "Taxable Bonds
Reimbursement Agreement") and the Direct Pay Letter of Credit Application and
Reimbursement Agreement between Bank and Borrower regarding the $3,420,000
Wisconsin Housing and Economic Development Authority Variable Rate Demand
Business Development Refunding Revenue Bonds, 1999 Series 2 (Zero Zone, Inc.
Project) dated as of August 31, 1999 as amended by the First Amendment, Second
Amendment and Third Amendment (as amended and as it may be amended from time to
time, and together with the Taxable Bonds Reimbursement Agreement, the
"Reimbursement Agreements"); and

WHEREAS, the parties hereto desire to amend the Credit Agreement and the Note.

NOW THEREFORE, for good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the parties hereto agrees as follows:

     1.  Interest Rate Rider. The attached Interest Rate Rider shall be the
         Interest Rate Rider for purposes of the Credit Agreement and the Note.

     2.  Cross Default. Without limitation of the demand feature of the Note,
         the following shall be a default and an Event of Default under the Loan
         Agreement and the Note: any default or Event of Default under either
         Reimbursement Agreement or termination of either Reimbursement
         Agreement.

     3.  Representations and Warranties. Borrower hereby represents and warrants
         that all of the representations and warranties contained in any of the
         Reimbursement Agreements, the Credit Agreement and the Notes are true
         and correct in all material respects as of the date hereof.

     4.  Conditions Precedent. This Amendment shall not be effective until it
         shall have been executed and delivered by the parties hereto and Bank
         shall have received the following, fully executed if applicable and in
         form and substance satisfactory to Bank:



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         a.   Third Amendment to Direct Pay Letter of Credit Application and
              Reimbursement Agreements;

         b.   Evidence of receipt by Borrower of proceeds of $1,500,000 in
              subordinated loans;

         c.   Debt Subordination Agreement;

         d.   Officer's Certificate; and

         e.   Borrowing Resolutions.

     5.  Entire Agreement. This Amendment shall constitute the entire agreement
         of the parties with respect to the subject matter hereof.

     6.  Applicable Law. This Amendment shall be governed by the laws of the
         State of Wisconsin.

     7.  Fees and Expenses. The Borrower shall pay all fees and expenses of
         Bank, including reasonable attorneys fees, arising out of or relating
         to this Amendment, or otherwise relating to the transactions
         contemplated hereby.

     8.  Effect of Amendment. The Credit Agreement and the Note shall remain in
         full force and effect as amended hereby and by the attached Interest
         Rate Rider.


 ZERO ZONE, INC.



 By:                                  _____________________________
    Jack Van Der Ploeg, President


                                      U.S. Bank, N.A.



 By:                                  _____________________________
                                      Caroline V. Krider,
                                      Vice President and Senior Lender



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                               INTEREST RATE RIDER

   This Rider is made part of the Demand Line of Credit Note (the "Note") in the
original amount of $7,500,000.00 by Zero Zone, Inc. (the "Borrower") in favor of
U.S. Bank, N.A. (the "Bank"). The following interest rate description is hereby
added to the Note:

   1.   Interest Rate Options. Interest on each advance shall accrue at one of
        the following per annum rates selected by Borrower (i) in the absence of
        a LIBOR rate election, the prime rate announced by the Bank from time to
        time, as and when such rate changes, less the Prime Rate Margin (the
        rate so calculated is referred to herein as the "Floating Rate"), or
        (ii) upon two (2) New York Banking Days notice by Borrower to Bank, the
        LIBOR Rate Margin plus the 1, 2, 3 or 6 month LIBOR rate quoted by the
        Bank (which shall be the LIBOR rate in effect two New York Banking Days
        prior to commencement of the LIBOR loan advance, adjusted as the Bank
        deems appropriate for any reserve requirement and any subsequent costs
        arising form a change in government regulation, from Telerate Page 3750
        or any successor thereto) (a "LIBOR Rate Loan"): If a LIBOR Rate Loan is
        prepaid, whether by Borrower, as a result of acceleration, upon default
        or otherwise, the Borrower agrees to pay all of the Bank's costs,
        expenses and Interest Differential (as determined by the Bank) incurred
        as a result of such prepayment. The term "Interest Differential" shall
        mean that amount equal to the greater of zero dollars or the financial
        loss incurred by the Bank resulting from prepayment, calculated as the
        difference between an amount of interest the Bank would have earned
        (from like investments in the Money Markets as of the first day of the
        LIBOR Rate Loan) had prepayment not occurred and the interest the Bank
        will actually earn (from like investments in the Money Market as of the
        date of prepayment) as a result of the redeployment of funds from the
        prepayment. Because of the short term nature of the facility, the
        Borrower agrees that the Interest Differential shall not be discounted
        to its present value. In the event the Borrower does not timely select
        another interest rate option for a stated period after a LIBOR Rate Loan
        expires, the Floating Rate shall apply. The Bank's internal records of
        applicable interest rates shall be determinative in the absence of
        manifest error. "New York Banking Day" means any day (other than a
        Saturday or Sunday) on which commercial banks are open for business in
        New York, New York.

   2.   Demand Facility. Notwithstanding the Bank's willingness and agreement to
        provide LIBOR Rate Loan(s) to the Borrower, Borrower acknowledges that
        this remains a demand facility and the Bank can demand payment of all of
        the Obligations at any time, including all LIBOR Rate Loans that would
        otherwise remain outstanding for their established term but for demand
        for payment by the Bank.

   3.   Prime Rate Margin and LIBOR Rate Margin. The "Prime Rate Margin" and
        "LIBOR Rate Margin" shall be determined based on Borrower's ratio of
        Senior Funded Debt to EBITDA, as follows:



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<PAGE>
<TABLE>
<CAPTION>
Ratio of Senior Funded Debt/
EBITDA                                      Prime Rate Margin                     LIBOR Rate Margin
-------                                     -----------------                     -----------------
                                         (subtract from Prime rate)              (add to LIBOR Rate)
<S>                                      <C>                                     <C>
< 1.50 to 1.0                                     1.625%                                 1.25%
=>1.50 to 1.0 but < 2.00 to 1.0                   1.375%                                 1.50%
=>2.00 to 1.0 but < 2.50 to 1.0                   1.125%                                 1.75%
=>2.50 to 1.0 but < 3.00 x 1.0                     .875%                                 2.00%
=>3.00 to 1.0 but < 3.50 to 1.0                    .625%                                 2.25%
=>3.50 to 1.0 but < 4.00 to 1.0                    .875%                                 2.00%
> 4.00 to 1.0                                      .625%                                 2.25%

</TABLE>


   4.   EBITDA "EBITDA" shall have the meaning provided in the Taxable Bonds
        Reimbursement Agreement.


   5.   Senior Funded Debt. "Senior Funded Debt" shall have the meaning provided
        in the Taxable Bonds Reimbursement Agreement.

   6.   Adjustment of Interest Rate Margin Amounts. The ratio of Senior Funded
        Debt to EBITDA shall be measured by Bank as of the last day of each
        calendar quarter for the period of four calendar quarters ending on such
        date and any changes to the LIBOR Rate Margin or Prime Rate Margin
        provided for above shall be effective as follows as to all then
        outstanding principal amounts:

        a.    for all outstanding Floating Rate Loans, on the first day of the
              month subsequent to Bank's receipt of financial statements
              evidencing a change in the ratio of Senior Funded Debt to EBITDA;
              and

        b.    for all outstanding LIBOR Rate Loans on the first day after the
              expiration of any interest period that is pending as of the date
              Bank receives financial statements evidencing a change in the
              ratio of Senior Funded Debt to EBITDA.

        Notwithstanding the foregoing, in case of any increase in the Libor Rate
        Margin or the Prime Rate Margin, such adjustment shall be retroactive,
        if necessary, to be effective as of the first day of the month following
        the date on which such financial statements were required to be
        delivered to Bank under the Credit Agreement. Each time Borrower
        delivers to Bank financial statements under which the ratio of Senior
        Funded Debt to EBITDA should result in a change to the Prime Rate Margin
        or the LIBOR Rate Margin, Borrower shall provide Bank with notice
        showing Borrower's calculation of such ratio and indicating the new
        Prime Rate Margin or LIBOR Rate Margin that should apply.

   7.   Calculation of Interest. Interest on Prime Rate Loans will be payable
        monthly on the last day of each month on the basis of the actual number
        of days elapsed in a year of 365 or 366 days, as applicable. Interest on
        LIBOR Rate Loans will be payable on the last day of the period on which
        the applicable LIBOR rate was determined, but for periods greater than
        three months, interest shall paid on the last day of each third month of
        such period and on the last day of such period. Interest on LIBOR Rate
        Loans will be calculated on the basis of the actual number of days
        elapsed in a year of 360 days.




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   8.   Default Interest Rate. Principal amounts remaining unpaid after demand
        for payment has been made or after a default or an Event of Default
        shall bear interest from and after the date thereof until paid at a rate
        of 2% per annum plus the rate otherwise payable.





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