G'day, If upgrading PSU, theres no point in buying a 400w from a 300w... Might as well look a bit further for hardly no extra cash and get something around the 550w mark. This way you will be a little bit more furture proof. When it comes to graphics cards, it depends on what card you are using, the 8800 needs 2 6pin connectors since it draws so much power and u need at least a 500w PSU for this, however any PSU will fit any board since these days you are giving more connector plus and options....shouldnt be a problem