It's a bit obscure, but it sounds like you want to play games on your Mac, so you want to use bootcamp to partition your drive to run a different OS so you can play games.
Er, what are you trying to choose between? The only OS you would be talking about is Windows, and while I suppose you could pick up a cheap copy of Windows XP on ebay, the only logical OS to get is Windows 7. The other available OS options (Linux, Chrome, et al) aren't specifically supported by bootcamp, and are even less gaming-compatible than OSX. You have no reason to consider them.
Windows 7 is a good OS and it's nice to have the option to use it, so it's not a bad thing to invest in. Software will be compatible with it for quite a while--I suspect it will be like XP in that regard, hard for Microsoft to move past. You will of course be compatible with all Windows games.