Well first off you have your Zalman mounted upside down. You are blowing your hot CPU air onto your GPU. So not only is it not cooling properly, but is making your GPU even hotter. My suggestion is to have it blow out the back, and have those two 120s at the top blow into your case, insted of having them suck out. The temps on that 8800 are not abnormal though. Its a hot card, that you are just making hotter. Even with the suggestion about the Zalman, its still going to be in the low to high 50s. A Zalman V900 will fix that right up for you.
As for the quad core. XP treats it as a dual core, there really isn't any support until Vista, and its a waste of cash anyway. Wate for the next gen of quads to come out, then pounce.
Cheers
Cameron
PS: For a first timer, you did a good job on the wires. When you get some down time and you are bored, jsut keep trying new configs until you get the cleanest case you can.
www.kustompcs.co.uk has a great gallery.