You want a decent 1200w psu amd 7950 or 7970s best value for money bang for buck so to speak a motherboard with as many pci slots as possible cheep stick of ram, cheap amd cpu, dont even need a case mouse keyboard or monitor or hard drive I use usb stick instead of a harddrive, you can pick up 7950s second hand from £150 a mobo about £50 cpu bout £30 used the powersuply is where you will and should spend your money as this is whats keeping you rig running