Computer runs a recent MSI Motherboard with all the expandability I could ever need [ don't remember the model]. It has a Intel Dual-Core 3GHZ processor [cause im too cheap for anything better right now] and 8GB zippy-fast ram. Oh and a 500 some-odd gig HDD. Graphics card is an Nvidia 9600 GT which still works fabulously for any of the modern games I've played including all the Crysis series.
Oh and I do this all on Linux ;-). Currently on the Ubuntu 14.04 LTS Beta 2 release but otherwise I've run Fedora, OpenSUSE, PCLinuxOS, Linux Mint, Sabayon, ElementaryOS, and many more.
I use the native Linux Steam client for some of my gaming [most recently Metro: Last Light] and other games native clients. Otherwise for games like World of Warcraft I run them using PlayOnLinux which is a nice little GUI for Wine.