Jose has a great post over on his blog that talks about how to setup a Hyper-V cluster using a file share instead of traditional shared storage:

http://blogs.technet.com/josebda/archive/2008/07/16/failover-clustering-for-hyper-v-with-file-server-storage.aspx

This is especially handy for anyone who wants to try their hand at clustering without investing in the hardware - as you can do this with three standard physical computers.

Cheers,
Ben