The latest version of this document is at http://fscked.org/writings/clusters/cluster.html. It is written in SGML.
I've read most of How to Build a Beowulf and I was left mostly unsatisfied. My goal in writing this paper was to do a better job. If you still want to buy this book, be my guest.
If most of this document was over your head, perhaps you should consult the Linux System Administrator's Guide and the Linux Network Administrator's Guide.
For more info on Beowulfs, consult the Beowulf HOWTO, the Beowulf Mailinglist FAQ, and Beowulf Underground.
For info on parallel processing in general, consult the Linux Parallel Processing HOWTO