Paul, with the parallel instalation you can repair all the registry hives by using a restore point from the damaged windows installation.
Read the following MSKB article:
Q307545 ??How to recover from a corrupted registry that prevents Windows XP from starting?
In your case, it?s easier because you can do it when you boot from the good XP and make the changes to bad XP from windows explorer.
Take the article as a skeleton because you don?t need to boot to recovery console. In essence, the new procedure should be:
1. Begin with ?Part Two? and check out the C:\System Volume Information\_restore{D86480E3-73EF-47BC-A0EB-A81BE6EE3ED8}\RPxx\Snapshot (on damaged XP).
Note
xx are numbers. You can see the files dates in order to have a clue regarding the newest restore points.
After you?ll find a convenient restore point, complete part Two.
2. From the ?Part One?, just delete the files: system, software,config,sam,security,default (not from a command prompt, but from windows Explorer). The files are under the
c:\windows\system32\config
path of the damaged XP.
3. Part three?s equivalent it?s to copy the files from the tmp folder to
c:\windows\system32\config folder.
Let?s recap:
You find a convenient restore point from the damaged XP and prepare the registry hives to a tmp folder. Delete the registry hives from the bad XP and copy the prepared hives (extracted from the restore points of the damaged XP) to the corresponding path.
Restart PC and let it boot from the damaged XP instance and if you?re lucky, it can boot. Regarding the data files from the damaged hard drive, the above procedure should left them intact because you replaced only the registry hives. However, for your piece of mind, you can copy the data files to the second HDD first.
Good Luck,
Cetin
Trying to unweave, unwind, unravel
And piece together the past and the future,
T. S. Eliot