You can pick up an 8800GT and it's a massive improvement, though their prices are still a bit high, or you can grab an ATI 3850 I believe as well.
I'd ditch that
RAM and pick some slightly cheaper DDR2 800. Also, I highly doubt you'll need anything more then a 500/600W
PSU
And I would definitely get some Artic Silver for thermal paste.
(Floppies are obsolete nowadays btw)
And I'm not too sure why you want a quad-core, the performance increase is quite minimal, even when multi-tasking, and the motherboard you picked doesn't even support quad cores
Compatible with all FSB1333/1066/800/533MHz CPUs except Quad Core
I'd also swap that motherboard for either a P35 or 680i chipset motherboard