Ubuntu is a great alternative to Windows on old or new hardware
1) Goto wwww.ubuntu.com and click Desktop for Developers
2) Click Get Ubuntu Now
3) Click Download
4) Choose your donation amount and recipients (nothing is allowed)
5) Click download now
You will now be downloading an installation copy of Ubuntu. Thus will be an ISO image that you can burn to a DVD and boot any machine and install Ubuntu multiple times as ubuntu does not have serial numbers.
You can even setup Ubuntu servers in the cloud.