Hello. I had the same problem a couple of months ago when trying to get my son's and his friends pc's to join our home network. Spent weeks trying to figure it out. In the end it turned out that both pc's had firewalls enabled. ( both were using pc-cillin anti virus with firewall enabled )
Now I have similar problem again. I just purchased new pc running ms2000. All other pc's on network are running xp. The ms2000 pc can access files from other networked pc's but other pc's cannot access this new pc. No firewall this time so I dont know what the problem is. So I think we have the same problem.