Slipstream it since you have XP SP1.

Download and burn SP3 to cd for future use.
http://www.microsoft.com/downloads/d...displaylang=en

Slipstream instructions:

Creating a slipstreamed CD

Slipstreaming WinXP with SP2

Installing WinXP & SP2 with one CD

Now once you have done that sfc /scannow will run correctly.