Fractal design 1000
Intel pentium G860
Radeon hd 5780 - I know my CPU may bottleneck this, but I can get one for an unbelievably cheap price (£85!)
550W XFX Pro Series ATX PSU with EasyRail™ Technology
500gb western digital HD
Yes, it's all compatible, but i rather get a new card like the 7850, which is better and for ~120£ and with two or three games free.
Also the xfx 450W will do for the setup, it will shave some for the card.