|Might try to take ownership of that file or change the settings to allow it. Some antivirus programs lock files to protect the system.|
I'd reload the entire OS from OEM media. Put on a good security suite. Update all service packs and drivers. Then learn and follow as many best practices to avoid this in the future. Simple things like running as a standard or limited user helps prevent this stuff. Goofy people turn off stuff like UAC.
A Pit Bull is like a gun you can pet. And there is no safety on it.