Laptops as servers = it WILL die.
I've seen it done countless times, and after a while something on the motherboard dies, and it's dead, good and proper.
Your best bet (IMHO) is to get a Mini-ITX system. You can get one of the older VIA chipsets, which can be passively cooled. Add to that a quiet HD (Seagate 7200.10s are VERY quiet), some RAM, and shove it in one of the little cases (they tend to have 'brick' PSUs, i.e. passive cooling) and you're laughing. Whack Linux or Windows on, and you have a nice little box, and they will run 24/7 quite happily. AND, they don't pull a lot of power. I've just built a little machine with
this board in
this case, and it pulls around 50 watts - and that's with three HDs in it. Admittedly, the fan on that board is horribly noisy, so I've replaced it with a different fan, and put a resistor on it to slow it down by about half. It's now pretty quiet. You could easily make something silent, or as near as.