I’ve been playing with Leopard over the last couple of days and just now figured out how to get Time Machine to work with unsupported shared drives (such as those shared by netatalk).
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1
What this seems to do is to create a sparse disk image on the shared drive, then mount it across the network. It’s not quite as nice as I would like, but it is a start.
Incidentally my inbox has been flooded with emails asking for a Leopard version of my httpmail plugin. I have been looking into it, but as to when I could have something I couldn’t really say.