I'm also interested on building a beowulf cluster just for fun, but for now I still live in my dorm so I am planning after my graduation to build one (depends on time and money), but for now I've found some resources for you so they may be helpful
:
http://www.cacr.caltech.edu/beowulf/.../tutorial.html
http://www.dl.ac.uk/TCSC/DisCo/TechPapers/Beowulf/