I'm building a myth box with some old and some new components.
I want it to run as cooly as possible (and as a result, as quietly as possible because of fans).

Currently, I have a DVD+-RW drive, an IDE hard drive for booting/system, a SATA drive for TV recordings/etc, a slim pci-e16 nvidia 6200 with 128MB, and a pentium D 2.8GHz 820 (dual core). 512MB of RAM at the moment, but I fully intend to add at least 256MB in the next month or so. There is one hauppage 150MCE, but I plan to add another, (one that has built in mpeg encoder).

So, how do I go about keeping it cool?

right now, my plan is to:
underclock the GPU (6200) with nvclock. I hope to bring it down to about 75% of it's original capability
underclock the CPU to 2.4GHz.
install a cheap, low power, but very quiet fan inside the case

Any other tips?

Use a PS with 120mm fan. Look at the airflow and make sure that it makes sense. Get a Zalman fan with variable speed for the CPU. Use mbmon to watch your temps.
This isn't a very good CPU if your goal is cool and/or quiet. From what I understand, the core 2 duo is a lot better with power, which translates to heat. The Dragon spec, for example, is based on a 939-pin AMD64 "venice", which is known for good performance/power ratio.

If I were you, I'd try to get the Dragon spec MoBo and CPU at NewEgg. Probably not much over $100 these days.

When keeping a computer cool, always think "airflow". Arrange the fans so that the air flows IN from one place and OUT the other. Often I see computer cases with all fans exhausing air. It's gotta come IN from somewhere!

One trick I like to use is to "underclock" a fan. I buy big 120mm fans from HSC that are 24V fans and run them at 12V. They still move plenty of air but are pretty much silent. You could use a 12V fan and wire it to a 5V supply for the same effect.

CPU fans have a BIG impact on the obnoxiousness of the sounds. I just replaced a Zalman fan (fan wore out) with an Intel stock socket 775 cooler. What a mistake!! The Intel fan has a very audible pitch which just resonates through everything in the box. I stopped by Fry's tonight and got a cheap ThermalTake TR2-MR1 RX fan (about $20 in the store). It does the trick. The processor can't be heard over the disk drive, so I'm at about the limits of what I can do.

Oh -- you can mount the disks with rubber bands to isolate them and make less noise. Or use rubber grommets which isolate the disk from the chassis. My current case doesn't allow for this refinement but Antec cases often do.

_________________
Do you code to live, or live to code?
Search LinHES forum through Google

Anytime you're trying to silence a pc, you have to look at the case first.

Thin aluminum and/or steel cases will resonate and echo everything that is bolted directly to them, including DVD drives, motherboard component fans, CPU fans, etc. It's best to go with a real HTPC case, plastic if you can get one, as they are quieter than a steel box. If you can't, then you go with quieter fans and see how many places you can use rubber and silicon grommets to isolate components. Case fans can often be mounted on rubber shafts designed specifically for this purpose, and the Antec cases generally include these starting with the Sonata series.

Even if your hard drives mount directly in a cage, you can put silicon grommets/washers just under the heads of the screws that hold the HD in the cage. Products like this one http://www.acoustiproducts.com/en/ultra ... mounts.asp come in handy. Check their site and others for more grommets. www.silentpcreview.com is another good resource.

If you really want to get anal, you can use sound deadening materials inside the case itself. Car manufacturers and high end car audio shops have been using Dynamat and other tar paper-type materials for years. Dynamat has a sticky backing, can be cut to fit case panels, and generally does a wonderful job but it comes at a price.

Further down the chain, some motherboards include tiny high-speed fans on the north and southbridge chips that love to make noise. Depending on the model, some of these are better replaced with high quality tall heat sinks instead. Zalman and others make chipset-specific replacements that do an equally good job at evacuating heat without the noise.

The CPU fan is pretty critical as well. Again, Zalman and others make big heat sinks with large, slowly rotating fans that help eliminate noise. Next take a good look at your video card. Most have small, fast fans that are usually noisy. Your best bet it to go with a passively-cooled video card with just a heat sink on it. It's a compromise, as the passive cards tend to be 'weaker' than actively-cooled cards, but you're only doing 2D most of the time with a MythTV box so you can afford to make the compromise. If you can't, again, look for a replacement passive cooling heatsink to replace the noisy fan.

That about eliminates everything. If you're really hardcore you can watercool your system. That brings it all down to a single 120mm fan on an external (or internal) radiator if you put the CPU and video card and possibly motherboard chips in the cooling loop. Generally the radiator fans have speed control knobs you can crank down to silent mode..but I wouldn't recommend doing this myself. Reason being that hot running hard drives and optical drives appreciate some air moving over them from the front to the rear of the case.