Stephen, I used to do quite a lot of this kind of stuff.Search the debian-powerpc and debian-boot archives for my name ("rbthomas") and "Boot-X". I posted (about Sarge timeframe) several "how-to" articles on using MacOS-9 and Boot-X to install Debian on a beige-G3-tower. It does not require boot floppies.
If you can't find anything useful that way, send me some email off- list and I'll see if I can find something that will help you.
Enjoy! Rick