Q: Do iBook "Clamshells" have a Boot Menu on startup?

Yes. You have to press the alt(option) key after hitting the power button see Apple support document

It works as long as no open firmware password ist set.

While most traditional Mac OS keyboard shortcuts appear to have a working

counter-part in todays OS X version, some later ones may not function in an

older hardware environment. (The link given above suggests Intel-based Mac.)

Older vintage advice and web pages that still exist for older Mac OS & hardware

are also worth looking into, since they offer a time-capsule from their day...

• Magical Macintosh Key Sequences - mackeys:

http://davespicks.com/writing/programming/mackeys.html#boot

• Mac Tips: The ultimate Shortcuts guide (MacOS 9.x pre-X)

http://www.silentway.com/mac-tips-ultimate-shortcuts-guide-mac-os-9

In any event, you've probably got it covered by now...!