Some backup utilities (like Roxio's Backup MyPC) provide an option to display all available backed up files for a drive, and a list of the available versions.
There doesn't seem to be any way to do that with WHS.
On Vista, there is a 'Previous Versions' tab listed in a file's properties window - shouldn't WHS be integrated into Vista enough so previous versions stored on the WHS would be displayed?
Though, it would be very useful to have this feature on XP also...