did you turn on the NetBIOS option? It is automatic and disabled by default, change it to Enabled and it should be able to connect to the other systems on your network. My brother had a problem like that and turning on the NetBIOS over TCP/IP worked with Non-XP machines.

Also did you turn on any of the "FIrewall" or security settings for the LAN connection? Chances are you may have shut down certain ports. Try an enable all on all ports to see what happens.