We are using Win 2K pro as a file server in a small office. I have a directory with about 5000 files in it. The old win 98 machines browsed it almost instantly but Win NT, 2K or Xp took 20 seconds or so. We tried all sorts of stuff but this was the final fix.
From the Microsoft website
177266 - Remote Directory lists Are Slower Than Local Directory Listings
We did the Regedit it suggested to the server and all is well now.