It sounds like you've fallen into the usual trap for post php 4.2.
From this point on the php developers (quite rightly) decided to not make post, and get variables global.
any of these variables can be referenced from the $_POST and $_GET arrays.
Alternatively you can just change your php.ini configuration file to set register_globals to "On":
register_globals = On
Or uncomment it if it's already there, be warned however that this is a security risk if you do not thoroughly test your code.
Hope that helps