If its a reference design HD6950 then yes (if your not sure just post a link to the exact model your looking at/have and I or someone else will tell you).
Watercooling your GPU will set you back about £230 (£80 for Pump +Res, £80 for GPU block + Fittings, tubing, coolant, Radiator, Fans....) Thats alot of money so I'd only recommend it if you after a quiet GPU and heavy overclocks.
Also you'll have to read up on watercooling alot and be prepared to do some maintaince every once in awhile.
well yeah i'll consider the versions with a good cooling system!
ohh and btw,
on the motherboard ASRock p67 EXTREME4 (B3) there is 3 slots for PCI EXPRESS 2.0,
do u think it'll work putting the video cards, one one the first slot, and the second on the third slot, leaving space of one slot?