quick hack attempt (you supply the product name variable):
$temparray = array();
$query = "SELECT *
FROM Cart_Temp, Products
WHERE Products.product_id = Cart_Temp.carttemp_product_id
AND Cart_Temp.carttemp_sess = '$sessid'";
$resource = mysql_query($query);
while ($result = mysql_fetch_array($resource)) {
$temparray[] = $result['productname'];
}
$description = implode ('.', $temparray);
Note: it would be better to only return 1 field in the query, since this is all that you are using, anyway. It saves resources and is good coding practice.