are all of these machines running the same Service Pack?
Yes, they are all XP SP3.
does your wifes computer have a password? if there is no require pswd upon login, you may not be able to been seen
Hers does not require a password. But the problem isn't trying to access her laptop -- it's her laptop being able to access our primary desktop. It can see the files, and browse everything on the C drive except for any of the User folders in the My Documents folders (and the Windows folder).
Thanks for all of the suggestions. I've been slow to respond because I've had other issues pop up, and in the meantime I've just been putting any files that she needs access to in the root C folder on the desktop.