Off topic: Linux vs Windows

Well, if you're interested in giving it a whirl you can burn a so called live CD. You can boot the machine from this CD and use Linux, no installation is required. You can opt to install Linux from the same CD if you then decide to. It will take some performance hit because CD is usually much slower than HDD but if you have enough RAM (say 4GB) and let it cache a few things it will run pretty fine. Also, all settings and that kind of stuff are not saved, this is not the recommended way to run Linux if you're going to use it on day-to-day basis, but it is excellent for a test drive

I would recommend Ubuntu, it has served me well for a few years. So well that I haven't had urge to check out the competition.

http://www.ubuntu.com/download/desktop

EDIT: oh forgot to mention that the regular install CD is a live CD.