If you are having a hard time finding any other pc's on your network on the vista pc make sure that "Password Protected Sharing" is disabled. Follow the instructions to see if it's on.
- Control panel
- Network and Internet (or Network and Sharing Center if you have "Classic View" enabled)
- Network and Internet Sharing Center
- Scroll down until you see "Password Protected Sharing" and tick it off.
I recommend to restart the computer for changes to make effects.
Then you should see Your vista pc's on XP and XP pc's on Vista.