For your first build, make sure you hear both ram module CLIP on your motherboard.
Also, make sure your fans are blowing on the good direction.
Last but not the least, come back if you have any trouble with your computer, it will be a pleasure to help you !
T: Your power supply as stated above, should be plenty for your 8800 ... If you plan on going for a second one, you might want to go for a 600-700 watts psu instead.
But for now, enjoy !