Ok so I have installed the Microsoft Security Essentials Beta, run a quick and full scan. I have to say its not to bad.
Looks like it takes about 4,184k of memory when running, and I guess thats not as good as some of the other free AVs on the market but it does seem to do the job.
I have taken a few screen shots below so you can get an idea of the different screens. It did find and flag Kon-Boot, so its doing something.