http://www.mini-itx.com/projects/cluster/

It's a FreeBSD cluster, but still interesting to see how he did it.
I would assume that you could easily do this with Linux.  Using the Cluster Knoppix Live CD (546MB 
image, could probably be stripped down), you could either have each node boot to the CD or use the 
authors method of having the node boot to microdrives.  I think a better/cheaper idea might be 
compact flash.  A lot of the hardcore MythTV guys are booting their frontend computers to compact 
flash.  

http://bofh.be/clusterknoppix/
http://bofh.be/clusterknoppix/clusterinaction.htm  for controller screenshots.

Brian Kelsay