overclocking is making things go faster than they are specified to go. Like taking the speed limiter(or whatever it is called) of a car or scooter.
I tend to reccomend 470gtx sli over a 5970 due to the far better performance and 3d surround cababilty. They are hotter though but that's isn't really a problem since it doesn't look like you will be OCing and nvidia cards can handle pretty high temps.
Also you can get an ssd if you remove the monitor bantracis mentioned since I stated you don't need one.
I assume you need a keyboard: the logitech g15, razer lycosa and sidewinder x6 are all pretty good choices.
for the rest bantracis mentioned a pretty good build.