Malcolm is spot-on - if you are reasonably conciensious, you should not get a virus or Spyware, with one major caveat. If you are on a network and you have publicly shared a drive (i.e., without hiding it by ending it with a "$"), some viruses on OTHER people's computers can reach your computer. To be safe, always hide your shares.
Another thing is that you have to do the Windows Update several time since there are some updates that require other updates to be installed first. To be safe, keep going back till there are no updates to be installed.
As far as AVG v. Bitdefender, I have to disagree with That Guy. I'm not sure where he got his info, but
Virus Bulletin gave AVG highest marks (free registration required), as did an
informal study at Tech Support Alert. Maybe he can shed some light on the basis for why he thinks AVG doesn't catch most viruses. After all, I'm always looking for something better!