What windows version?
Please post the info you get on the blue screen. (See the red boxes on the screen shot below.)
Have you tried the newest driver from Nvidia?
If your computer is rebooting automatically you can do the following to disable it.
Start the computer in normal mode and let it crash and reboot.
Tap F8 reaptedly during the bootup. This should bring you to the "Windows Advanced Options Menu".
From this menu select "Disable automatic restart on system failure" and press enter.
Select XP as the operation system to start and hit enter.