Try this, I found it a while back, but can't remember where I got it from:
1. Insert and boot from your WindowsXP CD.
2. At the first R=Repair option, press the R key
3. Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1
4. Enter in the administrator password when requested
5. Enter in the following commands (X: is replaced by the actual drive letter that is assigned to the CD ROM drive.
COPY X:\i386\NTLDR C\:
COPY X:\i386\NTDETECT.COM C:\
6. Take out the CD ROM and type exit