My page w/ the pop-up link has this:

<a href="../gallery_files/mini_cart.php" target="_top" myvar=<?php echo $fileid ?>>
<img src="../images/cart.gif" alt="Add to Cart" title="Add to Cart" name="add2cart" width="22" height="17" border="0"></a>

The page which I need to pass $fileid variable to has this:

<?php
$myvar = isset($_GET['myvar']) ? $_GET['myvar'] : false;
?>
<form METHOD="post" ACTION="http://www.wppi.com/store/buy.mv?Store_Code=78&Screen=DEN_TINYCART" target="shoppingcart">
<input TYPE="hidden" NAME="Product_Code" VALUE="<?php echo $myvar ?>">