I experiment a lot and i want to try to build a Beowulf system. Although i have read some things, i have many simple unanswred questions.
Question 1: Is Beowulf a specific cluster computer implementation? I mean is there a difference between the general idea of cluster computers and Beowulf?
Question 2: Is there a minimum number of coputers, which must be used? 16 is a typical number, but can somebody build a Beowulf system with 4 or 6 PCs?
Question 3: Must all computers have the same specifications? (RAM, CPUs, M/Bs, etc)
Question 4: Untarring or compiling something can be implemented on a cluster, but when i start a simple program (for example firefox, openoffice, eclipse) is the process implemented on one PC? When a new process starts, does it start automatically on another PC?

Beowulf is just an implementation.
You can use less than 16 computers. You need a head and at least 2 other computers.
They do not have to be the same specs, but it helps.
The combine is used for programs written specifically for clusters, you can't run office or games on it.

This is all from memory, it's been a while since I built one(3years or so.)

Perhaps if you go to the source.

http://www.beowulf.org/community/index.html

This might help. http://www.tldp.org/HOWTO/Beowulf-HOWTO.html.

Also if you want to set-up a cluster you might wanna check out this