There are many ways to implement Windows Server Failover Clustering with Hyper-V. I could actually find five unique methods to do it. Some of them will actually not give you a fully fault-tolerant solution, but most of them actually make sense in specific scenarios (even if only for demonstrations). In any case, just trying to understand and differentiate them will probably be a good exercise.
1 – Parent-based Failover Clustering with two physical servers
In this first scenario, probably the most common one, you implement Windows Server 2008 Failover Clustering at the Hyper-V Parent (Host) level. You will need some shared storage, like a Fibre-Channel or iSCSI SAN.
As you can see, this can survive the failure of one of the physical servers. In fact, if you have a redundant network and storage infrastructure (not shown above), you can have a truly highly available solution.
Additional details about this solution (including screenshots on how to configure it) are available at http://blogs.technet.com/josebda/archive/2008/04/14/snw-demo-windows-server-2008-core-hyper-v-and-failover-clustering-with-screenshots.aspx