Beowulf is a general name for clustering low-cost computers such as ["PCs"] to create inexpensive "supercomputing" capability. Many people use the Debian operating system on Beowulf clusters for several reasons, from the excellent system management tools to package availability.
There is a Debian Beowulf page at http://www.debian.org/ports/beowulf/ bla
There is also a debian-beowulf email list, with archives at http://lists.debian.org/debian-beowulf/
Beginners might be interested in how to StartaBeowulf
- or take a look at (PDF):
http://www.sintef.no/static/AM/vskoler/2001/notes/building_notes.pdf
Many Beowulf packages use UpdateCluster to simplify maintenance of their machines list
Whether for Beowulf-style computations or just a network of workstations, ?DiskLess provides a lot of tools that can ease administration for any deployment of 5-500 Debian boxes
Many parallel programs use MessagePassingInterface (MPI)
Many others use ParallelVirtualMachine (PVM)
http://wiki.debian.org/FAI is a tool for fully automatic installations of debian, and has been used for setting up many clusters.