Is there a way to install the newest build of Sp2 over top of an older build? I am currently running 2055 & want to upgrade. But there is a hitch. When I installed sp2 I accidently selected not to back up files. So now I can't uninstall it. When I try to install the newer build it whines saying I need to uninstall the older build.

I tried editing the registry to make it look like I have Sp1 again. But, windows keeps changing my changes back. I have WFP disabled.

That's impossible. Every beta SP2 build has had the option to backup files greyed out, so unless you deleted the $NtUninstall$ folder from the Windows directory, you should be able to remove it. You can try putting RC1 on top of it with the directions in the thread two below this one, but you're going to have the same issues ininstalling that one. Your best bet is probably a fresh format.