I have a couple of old computers at home and would like to turn them into servers for my friend's site, snooples.com where they are all cluster together (I think this is the right terminology), so if one computer fails, then the other one kicks in. This way the server will always be up. I just want to know if this is possible?

Also, if one computer is corrupted or becomes infected, will they all be infected as well(since they are clustered)? Then what is the best way to back up my data?

thank you