If you get the error:
Windows could not start because the following files is missing or corrupt
\WINDOWS\SYSTEM32\CONFIG\SYSTEM or \WINDOWS\SYSTEM32\CONFIG\SOFTWARE
1. Insert and boot from your Windows XP 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. cd \windows\system32\config
6. Depending on which section was corrupted:
ren software software.bad or ren system system.bad
7. Depending on which section was corrupted
copy \windows\repair\system
copy \windows\repair\software
8. Take out the CD ROM and type exit