OK Few things:
A. I'm building a computer now, and no im not waiting for conroe, why? Motherboard avalibility = BARLEY AVALIBLE! also, motherboards prices = OVERPRICED! and last reason: its barley known what ram will work with what mobo anymore, especialy with the conroe ones....
B. Go with an X2 4200, yes its only 200Mhz above but it gives you a better starting point if you're planning to OC up to 3Ghz or higher.
C. If you got the money [big if] go for an X1900XT >> Beats the 7900GT of all versions, and even a 7900GTX in most cases, however>>costy [also, ATi does NOT allow 3'rd party manufacturers like Sapphire, Asus and etc to overclock the cards @ the factory, and factory overclocks is a horrible thing!! I have heard horror stories of the quality of the voltmods and overclocks they do over there that would kill your video card right out of the box]
Thats about it, I'm personaly going AM2 too but whether to wait for conroe or not is a personal preference, but if you're gonna wait, prepare to wait a while.. a long while[at least a month or more] before the reasonable Conroe motherboards our out, and the hype will begin to settle down[and so will the prices... but that will take a while]
Anyways, you're setup with my slight changes would crank every games settings for at least 2-3 [and maybe even 4] years.
Other than that, youre setup if awsome, good luck with it, oh and i'd suggest the Gigabyte's 3D Aurora to accomodate that rig of your's