If you want to try out some multipath configurations, VMWare server has again a nice feature where you can make a vmdk available over more than one path.
If you want to try out some cluster configurations, VMWare server has a nice feature where you can share a vmdk between more than one VM, and since it support SCSI persistent reservations, you can truly simulate a real cluster. I have used this to deploy Redhat Cluster server as a test environment.