Hm.... I think I was going to build one. But finding compatible parts is hard. Assembly is easy.
I'd reccomend 2GB RAM. Corsair is another brand you can add to his list.
(I'm an Nvidia/Intel guy. Core 2 duo just owns AMD in heat and speed and price...)
Oh yeah, skip the 6600, just go straight to a 7 at least. With the 8800 out, the 7's are going to plummet.
Edit: Forgot to say ANTEC is the best case manufacturer..... They don't lie when they say they have 1000w power supplies... They are quiet and support 180 (?) mm fan slots all over the place. You will never over heat with one of those babies and 3 or 4 fans...
*ponders how much liquid cooling would cost*