Logon across router

I have a portable which can logon on to a domain when wired on site. It runs on Win2k with tcpip.
When it is either connected to the network via isdn to a router or on a remote network connected across isdn from its router to the main site router I can ping any other device by number, I can ping the domain server by name due to a host file and I can run Outlok to connect to Exchange server running on the domain server which is running NT sbs 4.5. However, I cannot make a drive connection or browse the network via network neighbourhood. I have tried lmhost file but without success. I may not be getting the scripting correct.