We’ve had nothing but awesome luck with Microsoft Security Essentials, but if you have problems you can try out this little utility that resets all the settings to the default values. We haven’t tested it, but the Windows Club guys usually put out good stuff. (And don’t use it unless you have problems!)
Well if you mean problems with it using up all the CPU on start-up and when trying to run other hungry things, then YES. Which is why I stop MSEngwhateveritis all the time and end up leaving it turned off. I’ll try it. Certainly can’t be any worse.