register_globals should be left off as it can be used to overwrite privileged variables if the PHP programmers are not careful. It's not always dangerous if appropriate care is taken, it's just unwise.
You can turn register_globals on via a per-directory basis with a php_ directive in .htaccess (or in php.ini for phpsuexec servers).
Alternatively, you can use $_POST to access the posted values, or the PHP extract() function to put them into globals.
The whole register_globals thing isn't exactly a success story - for years it's been bad practice and yet there's still a lot of code out there using it.