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. :)
