Command back - I was messing with the wrong boot.img.
_Update_ process on macs is easy:
Copy boot.img from the CD's drawer Mac_ppc32 to your boot: partition (mount it if necessay) by hand, then boot from teh CD and proceed with teh installation. That way worked fine for me, but be careful when messing with teh boot: partition, you can render your system easily to non booting.