My desktop has a 250W power supply currently. However, I recently installed an ATI 5670 and it seems to run alright, but I just found out the system requirements say I need a minimum of 400W. Does this mean just for the graphics card? Do I have to take in account all my other components when potentially purchasing a new one? Am I missing out on full performance by giving it less power? If so, how many watts should I purchase?