Here is my setup incase anyone is interested and is whisper quiet!
P4 2.8C with Retail HSF
Asus P4P800 Deluxe
2x 256MB Corsair
Antec Sonata Case
Radeon 9800 Non Pro
Winfast Leadtek TV Tuner
WD 120GB JB
I think one of the biggest is the Antec Sonata case. AThe hard drive sits on rubber things absorbing lots of the vibrations. The PSU included is a  True380W which is very powerful so even if you only need a total of 200W, it doesn't have to work as hard as say a 250W PSU and so the fan can spin much lower. The fan changes speed according to temps.
Then, the 120mm fan included can push 120CFM with around 40 to 50db. BUT, the PSU gives connectors for fans, which it controls based on thermal readings. The fan on my CPU is controlled by the "Asus Q-Fan" feature so it speeds up or slows down based on temperatures.
Oh yeah, with the Sonata case, you get rubber grommets for the fans too. I only have one outtake fan which throws the air inside the case out. Then there is a place for the air to come in on the front which has a filter on it which you can remove for cleaning or just not use. Personally, I have it there to avoid getting dust inside so I don't have to clean it.
Also, all my parts run at stock speeds and voltages, no overclocking at all. At night, the system seems really quiet I'm not sure if its on or not, hehe. I have to look at the blue lights on the front of the case. Oh yeah, speaking of the front of the case, the case also has 2 audio ports, 1 firewire, and 2 USB ports which is useful in many cases for me.