I bought a new computer some months ago and have tried to get used to the noise of it, but gave up recently. This is the configuration of my computer:
P4 1.8a with inbox HSF
Epox 4BDAE mobo (no fan)
MSI G4MX420D 64MB DDR (no fan)
Maxtor DM+ 8 30GB 7200rpm FDB
52x cd-rom LG
Codegen case & 300W PSU
I found in my "junkbox" a couple of 80mm fans, made by Jamicon and Spire. Then I replaced the PSU fan with the Spire fan @ 5v, cut away front and rear stamped grills and installed the Jamicon fan as exhaust @ 5v.
For the CPU fan I built a simple fan controller which lets me adjust its speed from below 1000rpm up to 2400rpm, most of the time it's running @ 1600rpm. The controller is installed in the top 5.25" bay.
The side intake holes on the case are closed with duct tape, so air gets in the case only from front, which helps cooling the hard drive.
MBM reports CPU temp 33/43C idle/load and case temp 24..29C. HDD temperature is 26..32C depending on room temp. The air coming from the PSU is slightly warm, but never hot.
The computer is right beside my desk, <1m away from me and the only sound I hear is the pretty quiet HDD whine and the almost inaudible whoosh of moving air. I'm sure the computer can be silenced further, but I'm on the budget and I think it's quiet enough for me.
Ghetto-looking on the inside, but who cares:
Front grille cut away, my ghetto-rounded floppy cable:
Rear view, fan grills cut away:
Front view, bottom plastic grille removed:
On this picture you can see my selfmade front USB port