In a previous blog post, Jose Barreto covered the storage options for Hyper-V and described the many choices between directly attached or SAN storage, fibre channel or iSCSI, passthrough or VHD, Virtual SCSI or Virtual IDE, etc.
If you missed that one, check it out at http://blogs.technet.com/josebda/archive/2008/02/14/storage-options-for-windows-server-2008-s-hyper-v.aspx

However, he didn't mention at that time the option to store your VHD and ISO files in a CIFS/SMB file server share.
Now he outlines how to use this additional storage option for Hyper-V with step-by-step instructions, a few screenshots and some performance tips.

Check all the details at http://blogs.technet.com/josebda/archive/2008/06/24/storing-windows-server-2008-hyper-v-files-on-an-cifs-smb-file-share.aspx