I've been attempting to do the same as you with little success...

I don't believe that the PowerBook is supported with 1.5. According to the 
model support page, it should be supported by 1.6, but the kernel crashes 
with a bad memory access very early on in the boot stage for me.

It might be possible to make a bootable cd out of one of the snapshots...

The other thing to watch out for is you need to keep OSX around in order to 
manipulate the bootloader (and kernel?) on an HFS partition. Unfortunately 
the released darwin code doesn't support the keyboard or monitor on these 
laptops....

Has anyone managed to successfully run netbsd on one of these things? If so, 
how? ;)

Thanks,
-w