Does System Profiler see the disk?
If not, unfortunately it's probably what it looks like your'e thinking: the bus on the iBook may not provide enough power.
A viable work-around to this may be to use a powered USB hub. (This is probably the cheapest option.) (EDIT: just saw your other thread -- bummer!)
In terms of booting, if you wanted it, is that OS 9 also has a weird HFS+ limit of roughly 200 gigs for a boot partition.
Other options would involve swapping to a powered desktop disk or a powered toaster or using a flash drive or SD card reader, which should fit within the clamshell iBook's power budget.
Other-other options may be to use a more modern, lower power drive such as a USB SSD or a more modern/thinner pocket HDD, although I say this and I haven't tested the 2TB pocket disk that works with my QS'02 on my iBook. (/366, but.)