I did it, but it was a royal pain in the butt. I just googled a bunch of different sites and tried a bunch of different things, and finally got it working. Sorry I can't be more specific than that, but I had to change registry entries and a whole lotta crap.
This looks like it has helpful info on how to get the Vista computer to see the xp computer. I do remember changing the workgroup name as it suggests.
http://www.computerworld.com/action/...icleId=9019179