before i go into all this junk below, your best bet would be plugging in a fan controller, turning everything down and seeing if you're satisfied with the noise and temperatures you get. if you're not satisfied..
the 500/600 watt seasonics are noticeably louder (mikec hasn't tested them, but forum users have noted motor noises from the 500/600 models) than the sub-500 watt models due to the ball-bearing fan, though still quieter than most any other fanned psu you could buy from antec, fortron, enermax, etc.
if you want a very quiet system without a huge amount of effort expended (though a fair bit of cash),
- get a thermalright si-97 cpu heatsink with a nexus or evercool 92mm fan
- get a seasonic psu of the s12 variety, the 380w would be an upgrade-safe model
- get a smart drive hdd enclosure
- get some evercool case fans
- get an aerocool vm-101 passive vga cooler to replace the whiny video card fan
- get a voltage-based fan controller
plug it all in and turn down the fans until you're satisfied. there are many things you could do for a system closer to silence, but diminishing returns will hit you and i'm not sure how much work you're wanting to put into this.
