Hi Soddit,
Go
here and install the Belarc Advisor. It will open a page in your browser and tell you (amongst lots of other things) what updates you have installed previously. Check to see if you already this one. There is no way on earth that M$ will have brought out a patch specifically for Sasser this quickly, so it may be that it's trying and failing to overwrite a previously installed update.
If you don't already have the worm, then an update for your AV will be enough to protect you until M$ sort this patch out. A quick trip to Googleland shows that it can cause more problems than it fixes.. just one being 99% CPU activity, and the recommendation to uninstall it anyway..
Hope that helps..
Cheers
Liam