If you don't know how to reinstall your OS or get rid of the viruses, I would strongly recommend a MacBook. Don't get the MacBook Air because it's slow, but the MacBook and the MacBook Pro are very good laptops. They may seem a bit pricey, but, believe me, Apple's computers are about the same price as any other equally equipped computer/laptop. With a Mac, you won't have to worry about viruses and they are super-simple to use (it's made so you can't mess it up). The newest Mac OS, Leopard, has been called the best operating system "for the vast majority of consumers. (PC Magazine)"
Post back what you get!
-------
I once heard the voice of God.
It said "Vrrrrmmmmm." Unless it was just a lawn mower.