Add Registry repair and editing to the list of Windows repairs you can make with a live Linux system, even if you can't boot into Windows. An Ubuntu Forums member shows how to make specific registry tweaks and fixes from inside Ubuntu.
User Melnichuk's tool is the same as we used to change and reset a lost Windows password — chntpw, or "change NT password". A "live", no-install CD or USB drive won't have it installed by default, but if you can connect to the internet, it's a very small installation you can make to your live system. With chntpw installed, and with your Windows drive mounted, it's just a few commands to get into the Windows registry:
chntpw -l /media/windows/Windows/system32/config/software
Move to registry branch you need, for example: cd MicrosoftWindows NTCurrentVersionWinlogon
and edit a key, for example: ed Shell
Obviously, you'd need to know which Registry keys you needed to tweak, but that's usually the case when you're manually removing a virus or trying to fix a specific, Windows-crushing problem.