How could I do this?
Actually, it was pretty easy. Here's what I did:
- Create a sparse disk image on iMac of 15 GB (Tiger Disk Utility has a GB and TB option now.) Give it the same name as the old, extinct, drive (eg. iBookDrive.sparseimage) - I think that may be pretty important.
- Mount image.
- In Retrospect Professional for Windows 6.5 open client view and go to tools. The mounted image appears as a volume. Select it so it's "known" to Retrospect.
- Do a complete volume restore to the mounted image.
Update 8/4: Well, it kind of worked as a boot image -- but only with some massaging and not all that well. OS X Disk Utility rejected using it to create a boot sector; some kind of error condition. Carbon Copy Cloner did use it, but the permissions were completely wrong (an issue with Retrospect, you have to disable permissions when doing a Retrospect restore, didn't do that on the image, I don't know if it's possible). I had to use Disk Utility to restore permissions and I safe booted. At that point the image did work, but some extensions didn't work. I gave up and used another image -- this was just an experiment to see if the image I create above could be used to clone a bootable disk.
 I'm using the Retrospect 6.0/Mac client on my Tiger machine -- a temporary option while I figure out how to replace Retrospect entirely -- but that's another story.