buy 667 ram and get the x1600xt not the pro as the pro sucks lol the 7600 gt or 6600gt would suit
apart from that all is fine
you dont need ddr2 800
my board (
gigabyte based on 945 chipset) allows you to change the ram multiplier so the overclock is smooth(might be worth checking the board does this)
good luck dude my machine runs best at 3.5 gig although it does run at 3.7