After some digging in Jaguar, I've just found the setting to change what workgroup you're found in from Windows clients, as well as the setting for adding a WINS server. It's in the Directory Access application in the Utilities folder; open that up, authenticate yourself, then double-click on SMB in the Services tab. The option to change workgroups or add an WINS server should be before you.
Note that you may have to restart the Windows File Services, log out or possibly even restart in order to change viewing/sharing settings. I did change my sharing workgroup successfully with just a stop/start in the sharing panel. Unfortunately, I don't have a WINS server to test with, so I don't know what's involved in getting the Finder's browser to browse a WINS server, or if it even works for that matter.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020830064040454