You would of course need a firewire based camera. Assuming you had one like the top Nikon, Software would have to be written to support a dirrect connection. None exists today. But that does not mean that we won't see it in the future.
I am sure a lot of pro digital photographers would love this.
You can of course use an ibook to act as the hub between these two devices. But that would kinda defeat the purpose of the ipod. (small and portable)