For XP, you can use “Tweak UI” to change your “My Documents” and desktop to the other drive.
Then you can just move your stuff across to the other partition.
This works out well, because if you ever upgrade your OS, all your documents are safely sitting on the other partition.
You can also achieve the same by hacking the registry … but … yuck.
In Vista & Windows7, it’s pretty easy to relocate your “my documents folder”. Right clicking on it will let you change the location.
Have you tried a disk cleanup?