I take it you mean, what do I need to run to make a thin client work? You'll need the X server on each of the thin clients, and you'll need whatever programs you want the users to run on the thick server.
P.S. I guess its too late now, since you can't relable a thread, but having two threads named "Thin Clients" makes it look like you double posted, which is against the rules. Plus, since people think you're double posting, they'll probably answer one and not read the other. You haven't done anything wrong, but I'd advise you to be more careful with the naming just so both your questions get full exposure.