Quiet laptop recommendations

If this is just for audio, you will want/need an external usb or pccard sound card rather than what comes with the laptop. In addition, the analog output from the laptop will be much quieter and more dynamic when the laptop runs on battery as opposed to AC. Another option is to run the optical digital out from the sound card to a DAC with your system. As for laptops, I use a HP with a Philips USB Dac for streaming internet radio (128k AAC) through Winamp, or for wirelessly accessing an iTunes library from a desktop server. As for fan noise, I think the cooler pad/ventilation suggestions below are excellent suggestions.
Also, I have heard that the AMD processors run cooler than the Intel, so you might want to check that out.

Good luck.

Some generic suggestions also: choose the slowest processor and the slowest hard drive available.. Particularly the processor will do wonders to the temperature. I would suggest the latest Intels at the lowest available clock speed! Use that with a hard drive that spins at 4200 or 5400rpm, but stay away from the fastest drives at 7200rpm or faster - they'll bring the heat up considerably (and noise as well).

Also, don't get a fancy specced notebook with a high tech graphics card in it. They too run at very high clock speeds and generate substantial heat. Hence, find yourself a notebook that's aimed at the business user, with as simple graphics as possible, a modern CPU at low clock speed. That'll work great! :)

A final simple tip is to run it on AC power and not on battery. Batteries get warm.. Pull it out and run on AC only. As has been suggested already too, use the most aggressive power scheme in the OS of choice, it'll bring down the CPU speed and such things, which conserves power. Less power means less heat = quiet. :)

Just set the laptop for "Max Battery" power mode and it will dim the screen and drop the processor speed. Make sure it's an Intel Centrio not a Celron to minize power consumption. I always elevate my laptop with something under it so it doesn't heat up as much... two pencils, one of those laptop coolers.

Watch out the new Intel Macbooks run really really hot...

Hard drive noise is mostly a thing of the past, so they're all dead quiet until the fan kicks in, then it gets dicey. My Dell D600, 3 or 4 years old now, runs the fan most of the time, is pretty loud even when the fan is still running on the low setting, and really loud when it switches to high. My iBook G4 is very quiet on low and still tolerable on high, but the fan rarely comes on even low and I've heard it maybe once switch to high. My wife's MacBook Pro runs the fan pretty frequently, but it's whisper quiet on low, and we haven't yet heard it kick to high.

I've owned many laptops and used/serviced many more (I'm an IT professional) and overall, I'd say PC laptops are generally louder than Mac laptops if the fan is running. If your father is ONLY using it for audio, the learning curve should be about the same unless he already has a favorite music program. iTunes, for example, is almost identical on both platforms.

All that said, it will also depend what he's doing. If he's only playing back files, then any laptop will run pretty cool because playback isn't very CPU intensive. If he's going to be ripping CDs it will generate more heat, from a little if he's suing straight AIFF files, to a lot if he's using high compression MP3s or AACs, which are very CPU intensive. Ventilation will play a role too - good air circulation will keep the fan from coming on so soon.

I'd suggest that you pick something that can be returned and then run the heck out of it to make the fan come on and judge for yourself. I've never held a dB meter up to any of my laptops, so I have no objective measure of the noise. What's tolerable for me may be way too loud for your father. Good luck with your search.

David