You will need shared disks. That can be SAN, but it can be a shared SCSI disk cabinet too. I even heard of just a SCSI cable from one machine to the other, so you do not need a cabinet. It just uses the disks in one of the nodes as a shared resource. Remember to give each node's SCSI controller a different ID!
Another option is using VMWare to set up a virtual cluster on just one machine. That is possible and done before. And even easier to manage from a training point of view.