Building gaming PC $800-$900

Hey guys,

This computer is getting old now and so I am looking for a new computer which needs to be able to play the latest games to a playable level.

So i am looking at gaming rigs from various websites and am interested in building my own to save money and maybe expand my knowledge/have fun. So my first question is, how easy is it to do, in particular over-clocking after it's been built for a reasonably tech savvy person but with no experience in hardware stuff?

So I want to spend $800-900, is this a reasonable amount to expect to spend, too little?

How do i go about deciding what to buy for the system? I have no knowledge of hardware so I haven't really got a clue except the basics of what i need, e.g. RAM, good benchmarking GFX card.

I found this website who made one for $700

http://www.tomshardware.com/reviews/value-pc-build,2506.html

Would it be a good or bad plan to just buy what these guys bought? If anyone could recommend parts for my price range, it would be great! Or alternatively, where is a good place to buy PCs online that would fit my criteria?

Thanks to anyone who replies, it's extremely appreciated!

Thanks