Virt-manager is compiled from mercurial tree but it isn't
working. I
don't know why. After run the virt-manager command, it was finished
without output error and the window wasn't created. If you need more
informations about ask me what informations I should sent.
I ran into that too -- make sure you have the "gtk-vnc" package
installed, it's a relatively new requirement of virt-manager and
there are no errors printed if it fails to load [1].
It's not yet a Debian package but you can get it from
http://sourceforge.net/project/showfiles.php?group_id=190580
-jim
[1] I'd provide a patch, but my python skills are severely lacking...