I'm having the same problem here. We have a Canon IR 5058 with an ImagePass G1 attached, it's a fiery (EFI) device. I've gotten the PPD working by manually browsing to it but we can't use any of the features we need, like printing to mailboxes and secure print. These features require the EFI JobNotes plugins, which don't run in 10.6 as far as I can see.
This is our central printer and integral to our work flow here, until a driver comes from somebody our entire organization can't upgrade to snow leopard. Any suggestions would be very helpful. I've tried manually editing the PPD file to try to hard code some default values in there so using JobNotes wouldn't be necessary, but I've had no luck.