Trouble booting 8.1 from USB stick on iBook G3 Dual USB

[halian%safiria.net@localhost]

I'm trying to boot 8.1 from a USB drive on my iBook G3 Dual USB (model 
ID `PowerBook4,1`), and I get the following error when trying to boot to 
it:

0> boot usb0:,\ofwboot.xcf netbsd.macppc method <load> not found, 
ihandle=ffbc5ac0 phandle=ff960fd0 load-size=0 adler32=1

LOAD-SIZE is too small
 ok
0>

What, if anything, am I doing wrong? or is it simply not possible to 
boot from a USB stick even via trickery?