Apple doesn't allow you to, and unless you're trying to put it on a hackintosh (a PC you specifically built to run OS X) then it probably won't run.
I second the suggestion for Linux. Ubuntu is a great distro. Depending on your hardware, it may take a little trouble to get set up, but once you have it working, it's quite a bit easier than in the old days of Linux. At least as easy as Windows, at least, and will make your machines perform a lot better. Give yourself a good day with nothing else to do, and install Ubuntu on them.