RAM: Kingston DDR3 2GB 1333MHz i5 Memory Module CL9 1.5V http://www.ebuyer.com/product/147903 £41 Will be easy to add another set later when you have a bit more money. Meanwhile you will get passable performance. Better to just start off with one 2GB stick as even after you go up to 4GB you will still have the further upgrade option of going to 8.
GPU: Palit GTX 460 768MB http://www.ebuyer.com/product/227181 £150
Much more powerful graphics card than the one in that link, which is the most important component for a gaming rig.