|You could try doing a System Restore|
To do this, boot from your Windows install CD and go through the install process until you get to the portion where it finds your existing system. It will then give you the option to do a restore.
Before you do that though, I would research the STOP error and the error code itself you see on her BSOD when it happens. It's entirely possible someone else has had this same issue and you might even find a resolution that doesn't involve a full restore.