A Google search results in lots of answers for you:

http://www.google.com/search?hl=en&i...=Google+Search

Including this Linux Clustering HOWTO from the search result:

http://ibiblio.org/pub/Linux/docs/howto/Cluster-HOWTO

And also this tutorial on the first page of the search result:

http://www.nwnetworks.com/basics.htm