Xp & 2000, Who is the Master Browser?

I set up a small Network (4PC`s). The Server is Win 2000 Pro. The four Clients are Win XP, I have joined them all to the same workgroup, they are all connected to the shared printer, and the internet connection is on one of the four machines
(Dial-up). The problem is each of them lose connection to the Mapped Network Drives on the Server (2000 Pro).
I think this has something to do with browser elections, Any Suggestions?