$basketArray = explode(",", $_COOKIE["basket"]);

for ( $i=0; $i<count($basketArray)-1; $i++) {
    $art[] = explode(":", $basketArray[$i]);

    $query = mysql_query("SELECT * FROM `catalog` WHERE `art` = '".$art[$i][0]."' LIMIT 1");
    $row = mysql_fetch_row($query);
    echo $row[1]; // Это id
}