The Internet is chock full of abandonware, free MMORPG's, and demos. I have Windows XP, so I'm not sure what all is compatible with Windows Vista. However, I've heard that Vista is not worth the money because it has a lot of problems and isn't compatible with a myriad of programs.
http://www.abandonia.com - Old games that can be legally downloaded for free
If you want to find some free games, Google "free games download" and a bunch of sites will pop up. Some sites require that you pay a monthly fee, but others might only want you to vote for them. It's hard to find a free download site that doesn't require you to appease them somehow.