If you know their names, try typing \\{Laptop name} on the desktop in a My Network Places window. This may not work as Vista has some network issues with XP at times.
Also, and I don't mean to sound rude, but make sure they're both on. So many people have on off and think that the files are just automatically "on the network" and the other computer isn't needed. I hate people sometimes.
Edit: You may also want to try putting everything onto flash drives or, better yet, Firewire drives if you have any. That can be faster, especially if you have a lot of traffic on the network and if you're using a hub rather than a switch or router.