Dont worry, those prices are too high AND you dont need to spend that much to get a top spec pc.

Something like this would do fine.

Processor http://www.ebuyer.com/product/131950
Ram http://www.ebuyer.com/product/98710
Motherboard http://www.ebuyer.com/product/113965
PSU(do not skimp in this department, must be good quality) http://www.ebuyer.com/product/114941
Hard drive- http://www.ebuyer.com/product/113430
Graphics card- http://www.ebuyer.com/product/120933
Case- http://www.ebuyer.com/product/118268

Think thats everything, now thats a top spec one incase your thinking fcking hell £300 for a graphics card it will last you a long time though

Or if you know nothing about pc's it might be worth spending abit extra and getting something prebuilt and delivered to you, because if you get your own parts you still have to find someone to put it together for you, then you will most likely have a part(s) that are faulty and need to be sent back.
Heres one from a website http://www.dinopc.com/shop/pc/viewPr...&idproduct=117

If you click on "customize" you can spec it to what ive suggested above(well almost)