Yes, it is possible, and cluster is the correct term for what you want to do. I don't have a link just yet for you, but I will research this subject. While I was in school, I knew a guy that built a linux cluster with 5 seperate computers- all acting as one server. I'm thinking of buying a few old computers, say 333MHz AMD machines and building one. PM me with any links you find on this subject.
Just Googled it.....this link looks good