explorer.exe, WerFault.exe, LogonUI.exe and others fail at boot

Hi,
A typical MS epic failure today. I was trying to install some web cam software that wouldn't work previously due to compatibility issues. However, I ran it as admin and it seemed to work fine. However, half way through installation, explorer.exe and rundll32.exe said they had to close. Also, it said that "memory location ....... referenced memory location ......... This memory could not be read."

The only thing I could think of was manually turning the computer off. Did that, and then they all did it again just before I got the logon screen! Ran a memory diagnostic off the RC install disc, and it reported nothing wrong.

I'm in XP now, which is fine, but can anyone tell me what's wrong and how to fix it?

Sounds like the driver still wasn't compatible, and if it installed then you'll need to uninstall it from within safe mode.

That was what I was thinking. However, Windows installer wouldn't work in safe mode and neither would Revo.

Did you try running the software in compatibility mode?(Xp SP2)

No, I ran it as an admin first (now a mistake!), as I know that can sometimes help, and the program came up with the message saying it was incompatible, not Windows.

I've had an idea, but it is at the limit of my knowledge!

I am currently running RegSeeker to see if it picks up and registry clashes, which might solve the problem.
Or,
I can get into the registry in safe mode. Installing things is all about copying and pasting the files in, and then making registry, points right?
So if I deleted all the registry files in the Logitech folder (Logitech being the make of the webcam), would it effectively uninstall the device and fix the problem?