Clearly this is going against the popular opinion on here, but I've never used a virus checker on any of my Windows machine and I've never had a virus. Actually I have used a checker a couple of times when I wondered if I had a virus (usually a Norton-derived one), but uninstalled it as soon as it had confirmed I was clean.
They are switched on all the time and are permanently connected to the Internet. I do always use a hardware firewall unless I'm traveling and using wireless in which case it is the built-in XP one. A few months ago installed Microsoft's Anti-spyware Beta, though it has yet to find anything sinister.
I do (carefully) download software. These days I don't use Internet Explorer or Outlook but I did for years.
For the last 12 months most of my desktop work is carried out on Macs, but various PCs are still on and used by me and others.
ThredNedul, as an aside, why the move from Mac to Windows? You don't hear of that very often.