Mulitier with Delphi 3.0

I want to build a multitier application.
But I have a problem. The client application could not find the
application server. I always get the error server failed.
When the application server and the client application runs on the same
machine I have no problems. If the application server runs on a
different machine I have problems.
Does someone know how to solve this problem. A friend of my has
also this problem.