Are there any other hard drives in the computer with Windows XP on it? That can cause the continuous repair at boot time issue.
If not, then there is something else going on, not related to NVidia. Memory corruption, hard drive issues or other conflicts in the hardware.
Are you letting NVidia or Microsoft update download and install new drivers?
If you are letting Microsoft do it, you will have just as many problems with AMD/ATI as you have with NVidia. I would not trust an update utility to update a video card driver. There are simply too many things which an go horribly wrong.