Have you check all the network setting on the windows 7 computer?
It should be something on the configuration of the network shares on the computer because you are able to access the drive from the rest of the computers.
Another thing that you can try to check is, are you able to access the windows 7 computer from the windows xp?
You can check also the firewall setting on the XP computer.
One thing that you need to be clear is that the issue is not with the drive since is working on other computers.