Good idea
“need cheap OS
Ubuntu (Linux) - free is better than cheap.”
This.
I’ve put it on a few friend’s compters who were in the OP’s position. I prefer Windows but if you don’t have the disks to reinsall it sure beats buying a new copy. It also depends on what you do with it. The people I gave Ubuntu to just used there’s to surf the Internet and do web based email.
+1 on Ubuntu Linux. I have been running it flawlessly on a (very) old Dell C400 laptop for years. In fact, I just upgraded to their latest LTS (long-term support) release 12.04.1 over the weekend.
You can also use Firefox with it, as well as the LibreOffice suite(new version of OpenOffice - Microsoft Office equivalent).