GET not working

Hello, I am working on a webservice for a client based on xmlrpc. Everything workes fine on our test systems. The client however has integrated the application and it does not fetch any get vars. The problem can be tracked down to getting the variable out of the url. We use $_GET[] to do this and it workes for register globals on and for off. But not on his server. They say that get routines wont work on their site since they use it for other "stuff". Apps that use them in a different way won't work properly. they use POST routines instead. How is that possible? Can anybody suggest on how to test this on our servers? What kind of configuration could that be? Thanx for any help, Merlin