I would go to overclockers.co.uk
put all the parts in the basaket you want and then give them a ring or email them and tell them you want it building to be sent to you, they add about £50-60 to build it, overclock it and send it to you, thats what I did coz im lazy.
literally just take it out the box, take out a bag inside the pc case and plug it in and its got all the drivers and stuff already installed and ready.