Neat little thing to customize the error messages. I know this is easy to all you pros, but this may not be so easy for a newcomer.

PHP Code:

$SQLErr = "Duplicate entry 'NAME' for key 'PRIMARY'";
    if (mysql_error()==$SQLErr) {
      echo "<p>Sorry, but that username is taken.  Please choose a different one.</p>";
    } 


Just change $SQLErr to be what your error message is, and change the echo inside the if to be your custom error message!

I always test for a match before trying to insert a record rather that letting the DB server/client raise an error.

However instead of trying to match the error text check the error number and if if it > 0 send a suitable message.

http://www.php.net/manual/en/function.mysql-errno.php
http://dev.mysql.com/doc/refman/5.1/...-handling.html