Microsoft iSCSI Software Target now available
All new OS have the iSCSI Initiator client already available out of the box. The server side component was only available for Windows Storage Server.
Now it is available for all other server types too.
How to use it with a Hyper-V Cluster read the blog from Jose Barreto
http://blogs.technet.com/b/josebda/archive/2009/01/31/step-by-step-using-the-microsoft-iscsi-software-target-with-hyper-v-standalone-full-vhd.aspx