Have a look at the forum Cheerio provided the link to. This route is the most likely to offer success. Follow the directions exactly.
I got one of these things about 8months ago. Ended up having to reinstall. They often seem to be installed by a trojan. (In my case, zolob trojan downloader..)
I always found Ewido had a much more effective search and clean function than the then MS offering. Another that appears to work exceptionally well is Spyware Terminator.
Don't be surprised if, when running Ewido, AVG suddenly farts at you and says "BlahBlah detected." It seems to me that Ewido can get into and scan areas that AVG cannot.
To Cheerio, any idea why the instructions on that forum say to disable the resident shield?