IF you want to play games, buy a console or stick with Windows.
I've heard and seen a lot of good about MacOS X (based on the BSD). But honestly, if you want to get something that you could install by a nice gui and then use, you can just download Fedora, Suse or Mandrake.
If you don't want to pay for the OS, that's abouyt the best you could get while still having it more or less easy to install.
I use Debian and extremely happy with this distro (and security updates by apt

) but it's not that easy to install.
Befire you decide, you can visit this site:
http://distrowatch.com/oh, and btw. if you want to see how it's going to be with the linux on your PC, you can give it a try without installing anything on the drive. Download a live cd distribution and just boot from CD to load the whole OS without touching your HDD. Knoppix or Suse live coudl be ok for you to try it.