Your new server might be running PHP 5 as opposed to PHP 4. That could be why your variables aren't being retrieved. A similiar update was needed on one of my sites. I'd suggest updating the code. Your life will be much easier moving forward. Just my personal opinion.
If you'd prefer a work around. From php.net/reserved.variables - Since PHP 4.1.0, the preferred method for retrieving external variables/B is with superglobals. Before this time, people relied on either register_globals or the long predefined PHP arrays ($HTTP*VARS). As of PHP 5.0.0, the long PHP predefined variable arrays may be disabled with the register_long_arrays directive.
For on page Error Reporting here are all your options.
// Turn off all error reporting
error_reporting(0);
// Report simple running errors
error_reporting(E_ERROR | E_WARNING | E_PARSE);
// Reporting E_NOTICE can be good too (to report uninitialized
// variables or catch variable name misspellings ...)
error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
// Report all errors except E_NOTICE
// This is the default value set in php.ini
error_reporting(E_ALL ^ E_NOTICE);
// Report all PHP errors (bitwise 63 may be used in PHP 3)
error_reporting(E_ALL);
// Same as error_reporting(E_ALL);
ini_set('error_reporting', E_ALL);
Good luck