A minidump is a symptom, not a cause. It is one method that XP can adopt when it detects a fault that requires a re-start.
If you click here you will see that by far the most common cause of re-starts at the moment is a nasty little worm called msblast.
Follow the advice in the thread to stop Windows from rebooting, then download the patch from Microsoft.
If that does not fix it, post back.
See also click here