You can back up the data on the user's profiles. I am not sure of the partitioning schema they did, but by default, user profiles go to c:\Documents and Settings\username. You can save that folder and restore it later. However, you need to restore it to wherever Windows is installed. As I said, I am not sure what partitioning schema they made on it.
Now,before you do anything, where is the Windows directory? Usually C:\Windows or D:\Windows. If you erase the partition that has the Windows directory, Windows is gone, accounts and all.