If this is a new installation of php, then it sounds like it could be...
I presume your just passing some variable in the url to instruct the script what to display?
after php 4.2 any of the variables posted in a form, or passed in a url are not registered (so you can't access $variablename).
you can either use the $_POST and $_GET arrays to find your variables, or you can change the register_globals configuration setting in php.in to:
register_globals = On
or just uncomment it if it's already there.
Hope that helps