Sorry about my last post.
I just forgot to "reset-all" (...)
Here are the results of my tests :
- clean/new floppies : boot successfull
- fat partition : boot failed
- home made CD : boot failed
- official iso : boot successfull, system installed ;)

Otherwise, i can't "DIR" from open firmware to any device but floppy.
dir ide0/disk@0 or any variation always gives me "can't open the DIR 
device". Does OF 2.0f1 really supports more than msdos (floppy) filesystem ?

Boot from official ISO was successfull when :
setenv boot-device ide1/disk@0:0
setenv boot-file NETBSD.MACPPC
reset-all
boot

Any idea about the "DIR" issue ?
Thanks