My case is a cheap no-name one, it came with a prebuilt amd athlon xp 1800 system, puchased in 2002 (not by me btw). I'm by no means a ' silence freak', in fact It never bothered me much, until I bought a ridiculously loud fan to replace the stock one on the cpu heatsink. Also I'm building a custom case for htpc use, wich basically started my interest in silent computing. On to my current normal pc
Stuff in the pc:
amd athlon XP 2200 (tbred A, stock speeds and volts atm.)
1024mb RAM, budget stuff
sapphire ati 9600XT 256mb
old and noisy 40GB maxtor
200GB samsung spinpoint
Coolermaster exteme power 430W psu
The case didnt have any case fans originally, but had space for one 80mm upfront, and one 80mm in the back. I tried some 80mm fans but wasnt very satisfied with them, so I started cutting
Now theres a 120mm nexus as exhaust, and a 120mm IBL fan (link, in dutch) as an intake. 
I haven't read much about these fans here at spcr, but I'd say its at least on par with the nexus. Its a pretty tight fit getting the 120mm fan at the back, in the picture its held in place just by tension, I can't realy feel it passing on vibration to the case(its running at 7v), but I'll mount it with some rubber later on anyway.
The original cpu cooler was pretty crappy, no pics of it, but it had a 80mm fan running at 3000 rpm. The worst part being that even at that speed it didnt cool very well. After reading alot of reviews I decided to get the Thermaltake big typhoon to replace it, partly beacuse its not very expensive here (33euro). Although its pretty scary to mount it at first, looking at that tiny tiny exposed core on the socket A processor I feel pretty confident with it now. Its performance is realy good, both sound and cooling wise, I'm using a fanmate with it for now, and even at its lowest setting it cools better than the stock one did.
To allow it to breathe some fresh air I cut out a 120mm hole in my side panel, and used part of the packaging of the heatsink as a duct.
The duct is mainly there to prevent the nexus from stealing the fresh air from the cpufan. Who said that this type of packaging isn't good for anything?
I also suspended my HD's like alot of you do here. I build a very ghetto style rack myself, using some 18x18mm wood I still had, and a few bits of some kind of plastic rod. I think I got those from destroying some kind of camping chair, but I'm not sure. They're very light, and very sturdy, and as they where just lying about catching dust I figured they'd be great for the job. Suspended it using clothing elastics I got from some local sewing shop. The unit looks rubbish, but works pretty well and was very cheap to make. Sorry for the crappy pics of this bit, its not my camera, and tbh I just kinda suck at taking pictures.
The videocard had a very nasty sounding little fan on it, wich started sounding worse and worse lately. After reading on this forum that there where also passive versions of the 9600XT sold, I decided I could easily make mine passive myself. I had an old athlon1800 heatink lying around, wich seemed perfect for this. I didnt take any before pictures, but it was a perfectly square unit of 60x60mm. I just bent all of the fins to allow air to flow passed it more easily, also took of two fins at the bottomt, to prevent them from hitting the pci slot below. To attach it I drilled two holes thru the base of it, so that I could use two bolts in the original mounting holes.
It seems to be working quite well, unfortunately my card doesn't seem to have a temp sensors, but it never feels hot, only warm. To be 100% sure tho I decided to move my intake fan to the inside of my case, so that it'd blow some air over the NB and ram, and also a bit over the vga heatsink.
Obviously this is still a prototype, pizzabox cardboard ducts ftw
Its not very clear on the photo, but the fan isnt touching the videocard or any part of the HD rack. With the intake fan mounted like that this heatsink doesnt even feel warm anymore, only a little at the base. Great succes on that part, especially since it cost me nothing The sound dampening stuff on the floor I bought from my local DIY shop, I mainly got it because I needed something to place the HDrack on.
The loudest thing in my pc is now the PSU, with wich I was in fact quite happy when I bought it (although admittedly I wasn't into the whole silencing thing yet when I bought it). Stopping its fan makes a huge difference in sound, so I suspect I need to do something about that.
With the cpufan being so close to the psu intake, I suspect that there's a fair bit of turbulence noise. Moving the psu would be the only solution to that I guess, but that would mean doing some pretty drastic cutting in the case. Do any of you know how easily I could swap the fan on it? It says on the box it has 'intelligent fan speed control' tbh I never realy noticed much difference, but would a fan swap 'override' that function? I'd rather not void my warranty by modding it tbh, but I guess thats the only option if I want to make it more quiet. Any thoughts or suggestions are very welcome, as I'm not sure of the best way to go about this one. One thing is sure tho, it needs to be silenced! This thing is now making the rest of my improvements feel sort of useless
To do:
- cable management
- make a new front panel (stock one is way too restrictive for 120mm fan)
- clean the case panels
- Silence the annoying psu
- make some kind of fan control
- replace stock NB heatsink, the current one is very small, and gets very hot to the touch.