Parker,

you have to do an manual install of NetBSD, because at the moment 
sysinst doesn=B4t support the option to use part of the disk as 
mentioned in the manual file.

Makoto Fujiwara has created a really cool page on installing NetBSD 
by hand. Have look under http://www.ki.nu/software/NetBSD/iBook2/
It helped me a lot for installing NetBSD on my PB G3 with an existing 
Mac OS 9 on a HFS+ partition.

Cheers, Chris