If I am 100% wrong about Service Pack 3 why are there so many threads from people who have had the same error?
Also if I am so wrong why did microsoft need to give the following webpage
http://support.microsoft.com/kb/156669/en-us ?
If you look at this page it CLEARLY states that a "service pack installation has failed"?
Most threads have had this problem directly after XP tried to automatically install Service Pack 3.
I suggest you do some research, like I did before you comment on what others know to be wrong.