Does the user on XP have an account on the 7 machine? If not, make one for them.
I have set up shared folders on my windows 7 box and have been trying to get to those folders from my XP laptop but I keep getting a login window to connect to the shared folder or map to a shared drive. I have tried the user account and password for both boxes but I still can't connect. What user name is it refering to? Oh, I am connecting through a router and I am able to remote to the windows 7 box using VNC.