Here is the example code I have
<form name="cart_4_ATC_shoes" method="POST" action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>">
<input type="hidden" name="cart_4_ID_Add" value="shoes" >
<select name="cart_4_Description_Add">
<option value="size 5"> size 5</option>
<option value="size 9"> size 9</option>
<option value="size 10">size 10</option>
</select>
<br />
<input type="text" name="cart_4_Quantity_Add" value="1" size="4" >
<br />
<input type="image" src="../../WA_eCart/Images/CaboSunset/Btn2_EN_addtocart.gif" border="0" value="Add to Cart" name="cart_4_ATC">
</form>
