I have been playing around with MSCRM4 lately. It has been interesting going. I had a problem getting the tax to reflect correctly, it was defaulting at zero. Eventually I found a solution after scouring the web for a while... see steps below…

Add the following code to OnSave and OnLoad events of quotedetails form

with (crmForm.all)
{
try
{
var dTax = (baseamount.DataValue - manualdiscountamount.DataValue) *15.5 /100;
        tax.DataValue = dTax;
        extendedamount.DataValue = baseamount.DataValue - manualdiscountamount.DataValue + tax.DataValue ;
}
catch(e)
{
        alert(e.message);
}
} // with

Don’t forget to publish your changes once you are done and to test.