Hi

By searching with Google I found that netbsd boot floppies are in fact 
in ustarfs format. So while a disklabel on the floppy or a dump of it 
shows a "a" partition as 4.2BSD, it's ustarfs.

So they cannot be mounted using mount it seems.

I have applied g4u patches to /usr/src and went into
/usr/src/distrib/i386/floppies

But you cannot use make inside this folder (a message from manuel
bouyer but from some time ago talks about it but it seems it no longer 
works with recent netbsd's sources).

Also tried to get for example inside blootfloppy
(/usr/src/distrib/i386/floppies/bootfloppy) but make there also
fails with :

make: don't know how to make /usr/src/distrib/i386/instkernel/
obj.i386/netbsd-INSTALL.gz

So I guess I have no other choice but to burn g4u as ISO CD,
dump it, mount it to put a new G4U kernel from 4.0_RC5 there,
and re-burn.