Linux is a FREE, open-source OS. It can literally run for years without crashing, is way more secure and safer than Windows. The only thing that prevents it from gaining the OS crown is its ease of use and simplicity.
EDIT>>> And becides, you can just DL it from another comp and burn it on a cd. Then just install it at the beginning. Or you can buy the different "flavors" (basically different manufacturers) for like 1/3 of Window's price.