As noted above this method is reliable only for backing up one box.
I have several clones of my C: drive.
One in a fire safe, one off site and the one installed.
I've not formatted and reinstalled XP for years now....it's too much hassle.

This happened recently;
NTldr not found
Press Any Key to Restart.Repair the XP installation?
Maybe. (In this case XP repair efforts failed.)
I pop in a clone HD and I'm back!
Do people still wipe and reinstall windows? J/K

Regards,
Sun