If the column type is TIMESTAMP, you can just use the MySQL NOW() function:
$query = "INSERT INTO aq_info (cust_name, cust_road, cust_city, cust_post, cust_telone, cust_teltwo, cust_fax, comp_name, comp_road, comp_city, comp_post, comp_telone, comp_teltwo, comp_fax, stamp) VALUES ('$custname', '$custroad', '$custcity', '$custpost', '$custtelone', '$custteltwo', '$custfax', '$compname', '$comproad', '$compcity', '$comppost', '$comptelone', '$compteltwo', '$compfax', NOW())";
If the column type is INT, you can use the PHP time() function, since time() returns an integer representing the current UNIX time:
$query = "INSERT INTO aq_info (cust_name, cust_road, cust_city, cust_post, cust_telone, cust_teltwo, cust_fax, comp_name, comp_road, comp_city, comp_post, comp_telone, comp_teltwo, comp_fax, stamp) VALUES ('$custname', '$custroad', '$custcity', '$custpost', '$custtelone', '$custteltwo', '$custfax', '$compname', '$comproad', '$compcity', '$comppost', '$comptelone', '$compteltwo', '$compfax', time())";