From: "Rich Gauszka" 

http://support.microsoft.com/default.aspx?scid=kb;en-us;878474

SYMPTOMS
After you install Microsoft Windows XP Service Pack 2 (SP2), your computer
repeatedly restarts. You do not receive an error message. CAUSE
This problem occurs if all the following conditions are true:
  a.. You installed the 32-bit version of Windows XP SP2 on a computer that
supports hardware-enforced data execution prevention (DEP), such as a
computer with an AMD 64-bit processor.
  b.. You installed hardware that requires the Mpegport.sys driver.
When you restart your computer, the Mpegport.sys driver tries to run from a
memory location that is monitored by DEP. You receive a Stop error that is
similar to the following:

0x000000FC (ATTEMPTED_EXECUTE_OF_NOEXECUTE_MEMORY)

Your computer may restart immediately if it is configured to automatically
restart when a system failure occurs.

--- BBBS/NT v4.01 Flag-5