There are linux distributions specialized on beowulf clusters, such as Rocks Clusters, which can facilitate the installation and administration of clusters. Unfortunately, rocks clusters (v. 5) didn't recognize the network cards of our computers. We tried the Ubuntu Server Edition (Hardy), which didn't recognize the CD-ROM. Fedora 9 recognized all hardware at once, so this was our distribution of choice.
Linux isn't the only choice, Solaris, AIX, DragonflyBSD, and many more systems have and can be used in clusters. The basic method is the same, often only with minor changes (e.g. Sun Studio instead of GCC).
For master and slaves, we started from vanilla installations.
A selected list of software: