Success.

I created a 735 MB volume on my iMac, and the SE was able to see it and write to it.

I shudder to share how I created the volume since it's sort of a particular solution, but in case someone cares....

I didn't want to lose the data/system I already had on my iMac's drive, but I knew that the end of the volume was empty and unused since it was a pretty fresh install (and large disk), so I skipped defragmenting the drive.

[1] booted a debian linux ppc install disk, exited to shell when I could.

[2] ran 'parted' on the iMac drive

[3] resized the mac partition, and created a new small partition with the free space at the end of the drive.

[4] rebooted with a Mac OS install disk

[5] using the apple disk utilities app, under the preferences menu made the new volume 'mounted at boot time'

[6] rebooted (original system on hd)

[7] The system asked if I wanted to initialize the volume, and I did.

[8] ta-da!