About a year ago I posted a problem (#143285) about a peer network with WinXP, 95 & 98 PCs that couldn't exchange files. I got a lot of useful suggestions and posted the solution in #144903 in the same thread. In brief, we had to Enable Netbios Over TCP/IP. We just recently replaced our ancient Win95 file server (really just another PC on the net) with a Win2K Pro(SP4) PC and found the same problem, i.e., the Win98 PCs could'nt "see" the Win2K server. After much head scratching and experimenting we found the solution. We used an LMHOSTS file on the Win98 PCs. Our problem was the network's inability to resolve the computer's netbios names. Below is a quote from the first two lines of the LMHOSTS.SAM file in Windows.

# This file contains the mappings of IP addresses to computernames
# (NetBIOS) names. Each entry should be kept on an individual line.
We also put this file into our WinXP PCs and now everyone cane see everyone else. Hooray!

We still don't have a clue about the cause, but at least we now have a solution. Some posts on related topics (slow response accessing the server) indicated the hub (ours is at least 5 years old) may be at fault. One post said that replacing the hub with a switch solved his problem after he installed SP-1, but this seems a stretch for our case.
I hope someone finds this info useful. Since Search is still not working this link should take you to the original thread.