EDIT: Oh, before you try all that other garbage I mentioned below, make sure you are in the same workgroup. It could be that simple.
Well, if you aren't running a novell server or network, pull the IPX protocol. Windows 2000 and possibly XP (don't know much about it yet) use a thing called bindings to assign protocols to network adapters. Problem is that TCP/IP is installed by default out of the box and when you add another protocol it puts it higher up in the list of protocols to use first, meaning your comp is going to try to find something with IPX first, not the best situation on a Windows network. To check all of this out, in Windows 2000, right click on My Network Places and then click on properties. In the menu above click the Advanced section and choose Advanced settings (genius names they come up with....). In the Connections section make sure that Local Area Connection is selected and then move NetBEUI above IPX and then move TCP/IP to the top of the list. You could use NetBEUI alone as there is basically nothing to configure there, but TCP/IP is the most versatile and widely used protocol. I have been told by a friend that uses XP that he couldn't get his computers to talk in his home lan until he went through a networking wizard. Might try that......
Are you using DHCP, either through a router or a server? If not and you want to use TCP/IP then you need to assign IP's to your computers on your own (192.168.1.2, 192.168.1.3, etc. Leave .1.1 for a router if and when you eventually get one, as this is the traditional IP address of a router).
Tell us more about what you want and your setup. Maybe we can help more....