contrary to popular belief, there are malicious codes out there for linux and there are anti-virus programs out there as well.
two things make most linux distros resistant to virii.
1. you actually have to input your password to make a system change, windows only asks if it's 'ok' and most idiots hit the button even before reading the pop-up.
2. literally everyone and his mother is on windows, making it logical to make a program that targets as much users as possible.
I'm not saying I hate windows, I use both linux and windows. even if windows is just for games and everything else is linux.
seriously, the first thing that I encountered in vista, and this was well passed the initial screw ups of the OS, was an error that made me need to reboot.
there's WINE too, and most recent games run decently with it.