you can get 'AVG free edition' works great take a system scan and also everytime you enter a folder if AVG finds a virus when you enter it you can enter heal it or put it into the virus vault.

other things might be spyware try 'search and destroy' its free and works also great.

is you system old? long time since defragment?

if you still got the antialias error, check your video driver maybe its on inside the drivers you can turn it off.

what video card you got by the way?

even if you got direct 9.0C it may be a old version, download via microsofts site