for the search form:
Change the name of the select list to ProductCategoryID
<select name="ProductCategoryID" class="input-med" id="ProductCategoryID" onChange="document.filterform.submit();">
and add a hidden element named WADbSearch1
for the sort form, the value of the options should be the name of the columns, instead of:
<option value="test.php?sort=ProductSKU" >SKU</option>
use:
<option value="ProductSKU" >SKU</option>
then set the method of the form to get:
<form method="get" name="sortform">