In the menu.php page after the menu has been modified, change line 77:
<li><a href="<?php echo($assumedRoot); ?>Products_Results.php"><?php echo $row_menuwriter_productcategories["CategoryName"]; ?></a></li>
to:
<li><a href="<?php echo($assumedRoot); ?>Products_Results.php?Search=true&CategoryID=<?php echo $row_menuwriter_productcategories["CategoryID"]; ?>"><?php echo $row_menuwriter_productcategories["CategoryName"]; ?></a></li>