As for components, I would take a look at some of the OcUK pre-overclocked bundles such as this:

http://www.overclockers.co.uk/showpr...id=339&subcat=

Add in a last generation graphics card such as:

http://www.overclockers.co.uk/showpr...odid=GX-079-GW

And a new power supply (if you need one):

http://www.overclockers.co.uk/showpr...odid=CA-111-AN

And a bigger HDD

http://www.overclockers.co.uk/showpr...odid=HD-054-SA

Use your current case and optical drive, and you've got a very capable PC for under £450, will play almost anything on max at your resolution.