CPU for o/c would be Q9550S, if no o/c then QX9770, may cost a few £££.
Will support any current video card, if your psu has enough wattage and power connections.
Memory @ DDR2-800 you can fit 4x4GB G-Skill F2-6400CL5Q-16GNQ
memory @ DDR2-1066 you can fit 4x2GB Geil GB24GB8500C5DC
Of course, you need to be running a x64 o/s.