I am about to build a new PC. My goal: as quiet as possible (surprise).

In the PC I will fit:

An Intel Core 2 Duo (E8200) CPU with Scythe Ninja cooler (preferrably passive)
A motherboard with onboard graphics OR
A motherboard without onboard graphics and ATI RADEON HD 3450 graphic card
A single 3,5" HDD (Western Digital Green Power 500 GB) mounted in a 5,25" drive bay with rubber thingies
2 GB RAM
A DVD-burner

I will not game. I will not overclock. I will, however, watch and encode MPEG4 and H.264 videos. I don't expect my system to generate much heat or draw a lot of power. I hope to be able to run the system with a maximum of two fans: one in the PSU and one case exhaust fan (both must be 120 mm).

Until recently I thought I would be getting the Antec P182 as case for my system along with a Corsair VX450W PSU. But after reading here in the forums I am now in doubt if this is overkill for my needs (spacewise and with regards to cooling capacity).

Will a smaller, cheaper case be sufficient for my needs and just as quiet? I considered the Antec NSK 3480, but I don't know if the bundled PSU is as quiet as the Corsair VX450W or if the ressonance is as efficiently dampened as in the P182. I have also been considering the Antec Sonata SOLO.

The P182 + Corsair PSU is a quite expensive solution compared to the others. I don't mind, however, spending the extra money as long as I get the quitest case. But maybe it is silly to buy a big P182 case if I can get something smaller and cheaper that is just as quiet. This is especially true if I have to swap all of the Tricool fans of the P182 to achieve quiet operation (and from what I have read in here, this could very well be the case).

Should I go for the P182 as originally planned, or are there better alternatives for my needs?

For a small low powered PC like yours, you should go with the Antec Solo. It'll be as quiet as the P182 with no fan in front, no fan on the Ninja, only the back fan to cool the CPU.

Also, it comes with a good hard drive suspension system.

It should like this :
http://www.silentpcreview.com/article781-page3.html

in your situation, i'd definitely get the 3480 as a starter.

whether or not you stay with the built in PSU is a different matter. but i'd personally go with an matx board..either with onboard graphics (g33/g35 chipset) or without onboard graphics, with a hd3450/3650.

the 3480 will still allow you to put in a VX450 if you want, but i've heard the antec earthwatts...they're realllly quiet.

Thank you for the link - interesting reading.

Now it's decided: I will go for the Antec SOLO along with a Corsair VX 450! I will try the stock fans to start with, and if the system is too noisy for me, I will swap the fans.

Can someone confirm that a Scythe Ninja will fit inside an Antec SOLO?

It will fit like the hand in a [glove], I got myself an corsair VX450 together with a Antec Solo (black) a couple of months ago, and it works perfect. A little bit of coil whining from the PSU after some weeks though, wich I can hear with Fans on low settins and not any other sound from other sources. So am going to RMA the PSU soon enough.

With a system like that you should really consider going mATX. And If the P182 is overkill, that 450W PSU is also overkill. You would be well served by an S12II-330 for example.

The seasonic mentioned should be a good buy though the corsair is just as efficient at low load despite the higher rating.
The tri cool fans are a bit too fast even on low but maybe you could drop their speed further using the motherboard controls. Otherwise the solo is a good choice, made of thick, 1mm steel just like the p180.

I was under the impression they were both made of 0.8mm steel and only the lower drive cage of the P182 uses 1mm steel.

i'd still get the antec NSK3480... the included PSU will be more than plenty for such a low power rig...and the earthwatts PSU's are really quiet.

i'd switch the rear fan out for a 800 RPM slipstream, and get a zalman fanmate for tuning it down to silence.

I have a good feeling about the SOLO, so I will stick with that even though a 3480 may be able to solve my problem.

I know that a Corsair VX450W is overkill for my power needs, and I would be happy to buy a lower rated PSU if it is just as silent. But from what I've read in the SPCR reviews, the VX450W is the most quiet of the "low-rated" PSU's you can buy. Is this true, or is the S12II-330 just as quiet? Or are there other lower rated silent PSU's that I have overlooked?

FYI the Corsair VX450W and the Seasonic S12II-330 cost the same where I live.