I can't remember what a Sparc 10 looks like, but they will need at least 2 network adaptors, one for the cluster heartbeat and 1 to your real network. The heartbeat link requires a cross over cable. Ideally you should have 2 of each on seperate cards for resilience, but as this is only a test, 1 of each will do.
You need to be able to connect the multipack to both servers.
You could use Solstice Disk Suite (which is on the Solaris media) to configure the shared disks to give simple mirroring. But again for a test this can be left out.
However you will need the clustering software, either Veritas as Chacalinc suggested, or Sun Cluster 2.2 or 3, which I prefer. This, I suspect, will have a cost.
Steve