Getting a new PC? Almost any quad core with somewhat decent GFX* will be fine. For 3D or big screen (higher res than 1080p) full 'oomph' you might want to scale up a bit, towards the 'alienware' or beyond.
If you have only a few years old "run of the mill" quad-core PC with somewhat decent (for gaming) GFX and at least Windows 7, you should be fine.
* Nvidia - go for GTX 600 series or newer, aim for at least 650 or higher, bigger number packs more punch in same series (e.g 670 beats 660, but 470 beats 620), and even more with a "ti" added to the end
* AMD - go for HD 7700 series or newer or R7 - R9, bigger number packs more punch in same series, even more with an X added to the end