XP won't boot after installing critical update

My pastor called to ask if I can help him with a problem, and I'm stumped. Details are sketchy, but here's the gist of it:

1. He has Windows XP Professional (upgrade from Windows 98) running on an HP Pavilion. I can't recall the model number/processor, etc. He has 2 hard drives. Both were running fine before this problem.

2. Today he went to Windows Update and downloaded/installed critical update(s)...No, I don't know which one(s).

3. It downloaded and unpacked the files and started installing them, but then his PC hung up and he had to reboot. He couldn't warm boot it, had to cold boot.

4. When he rebooted, it started going to the Windows XP startup screen, but then went back to the setup screen, then to the startup screen, then to the setup...and endless loop.

5. He even tried booting from the Windows XP CD, bypassing the hard drives, and it still did this loop.


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5. I walked him through going to Safe Mode, and we tried restoring the last good configuration. No luck. We get the same loop of startup screen/setup screen, etc.

6. If he tries to just boot to Safe Mode, same thing.


Further info:

He gets an error when he tried going to Safe Mode, many lines, one of which said something about multidisk and r-disk?

Like I said, he has two hard drives in there. The one, the original, was acting funny, and he bought a new one and made it primary. He has the old one slaved to the new one. When this all happened today, he tried disconnecting the old/slaved HDD and rebooting, but the cycle just happened again.

Aside from doing a reformat, does anyone have any suggestions?