If you want quiet then you don't want ATI, the power draw from their high end GPUs is incredible, some sources quote them as drawing 120W at full power, that's right up there with a prescott. Wait for the 7900 refresh, they'll run cooler and thus will be much easier to silence.
DFI is out for low noise, you'd have to swap out the chipset cooler and there isn't enough room on some of the boards for a passive solution. Asus do good passive motherboards, i think abit do some too, if you're not overclocking then it doesn't really matter which board you pick in the end.
P150 is the quietest stock case around, suspended HDs and lamminated construction. With a bit of planning you can make it dead quiet. For a higher spec system the P180 is a better idea, still a very good case for low noise. Lian Li also do top notch cases that are as good if not better, but i don't know the model numbers.
AMD CPU Dual core, the higher the better.
A8N32 or other passive motherboard, the 32 is overkill unless you get SLI, which is a bad idea unless you're doing it from the word go (imo)
7900GT or GTX Buy from eVGA and swap the heatsink off for a quieter one if nessisary. SLI the GTs if you want really high end gaming performance.
2GB Low latency RAM, with your budget you might as well and it does improve things a tiny bit.
Samsung spinpoint hard drives, the quietest 3.5" drives around.
Seasonic s12 PSU 500W. Very low noise, you might be able to use a passive/semipassive like the antec phantom, but that depends on your case choice.
Swap out all case fans for nexus 120mm 1,000rpm orange fans.
CPU fan depends on your case and specification. The Scythe ninja is very low noise, but the tuniq tower would be worth a look.