Hmm... make sure you have AppleTalk installed in your LAN settings. Other than that, I don't really remember how I used to do it (having had a working mac in about 4 years)
Well, I'm on a win2k machine, so I'll tell you how to do it on there.
Go to start->settings->network and dial up connections
get properties on your LAN connection
Where it gives you the list of what components are installed for that connection (TCP/IP, NetIOS, etc.) there would be AppleTalk listed as well if it is installed. If its not there, click on install below that list, then install a Protocol. I think you have to have your windows CD in to install it, but I'm not positive about that. Anyway, you should have an option of Appletalk to install, so... install it.
Are they running OSx? see if they can run samba if they can, I think it either nativly supported or there is some underground movement to make it work.
What OS is on the Mac? 10.3 (Panther) has automatic support for Microsoft Networks. I was able to serch by IP address on my WinXP machine and find my new iBook easly that way.
Also there is a new thread over in the Apple Forum named Networking between PC and Mac?. As said by Methodical in this thead "the basics of this is in the faq..." which can be found HERE.