I have a small network of an XP and a 2000 box. I have them set up on the same internet connection, through the same router. How would I allow access from XP to 2000 and vice versa?

Once you do that verify that both of your computers are in the same subnet. If you don't know how to do this just send the IP addresses of both computers.

Then what you need to do is right click on network neighborhood and go to find computer and type in the computer name of the other computer and it should find it. If it doesn't find it try using the IP address of the other computer. If that still doesn't work try restarting both computers.

By the way the workgroup really doesn't matter the thing that matters is that they are in the same subnet/network.

You should also create Sharing on each machine to allow access, and on the 2K box you need to create a user name and pwd the reflects the the Login on the XP box, on the XP box it is much easier just allow sharing to who ever is on the network.