Have to say although it's not a bad build I would change pretty much all of it, sorry
Here is what I would buy though.
Intel E5200 Pentium dual core ~£55 : You don't really lose an usuable speed and save about £50. It still overclocks like a freak anyway.
Scythe Ninja II or Xigmatec tower cooler to sit on top
~£20 - £30.
Asus P5Q .. PRO ~£90 probably, unless serious overclocking is involved there is no call for the Deluxe.
4GB PC6400 Corsair XMS2 ~£40, chip as chips and all the speed you will ever need from it.
Corsair 520W HX PSU ~£65 no need for anything more than that.
Coolermaster CM-690 ~£60 great case, cool, quiet and very easy drive/cable management.
640GB Western digital AAKS ~£50 One of the fastest and quietest out there.
Optical Drive (pionner maybe) ~£15
The montitor you picked is great ~£135
ATi HD4870 ~£180 (massive overkill but just to give you an idea on price).
Windows ~£65
Comes to less than £800 using rough scan prices.
It will be super speedy and should be very quiet too, espeicall if you get a graphics card with a decent quiet cooler on it. An HD4850 will save another £50 and won't impact gaming performance particuarly at this resolution.