Crikey, that's a while back, Jeff
Basically, we are looking at this line:
<FORM method="POST" action="search.php" name="productsearchform">
within which is "search.php" - so what you need to do here, is change the link so that wherever you put this form, it can still find search.php
Maybe adding
http://yourdomain.com/search.php
or
http://yourdomain.com/store/search.php
or ../search.php
something like that, just so it can find the file from wherever it is.