and as 6 pin is 75 Watt, and 8 pin is 150 Watt you really would want to do that with that PSU.
Most GPUs use 2 6 pin connectors to get to 150W, instead of an 8 pin, because of all that multi 12V rail BS that went around. You should be fine using a 2 6 pin card with an adapter though as that would only be a 150 Watt card
Hmmm can you recommend me anything? i was looking at the 6850 but i dont know if thats the best my psu can handle..