With 3 Pentiums III and a single power supply, you can make a low noise and consumption cluster. This can be done with a single hard disk and packed in a standar PC-tower if the hardware is appropiated.
I made this kind of "how it is made and how it works", explaining the openMosix practical functionality and a real example of how can you take advantage of your old hardware.
English version is here:
This web server is closed at night (Spanish hour) and could have some off-line moments at day. Hope you find it useful.