I'm actually working on a 6500 right now

I just had the exact same problems. I finally got to boot with a boot 
floppy: here's how to make it!
get the netbsd.INSTALL.gz of release 1.6 (on netbsd's ftp)
get OFWBOOT.XCF from release 1.5.3

format the floppy via VirtualPC (formatting in the mac won't work since 
it places invisible files that take a couple of k, that will prevent 
you from putting the files on the floppy)

boot in the OF

type
0> boot fd:,\OFWBOOT.XCF

it seams to have frozen at some point but you have to let it go a while 
(you hear the floppy making just a little noise)


then you should be in the installer

now that's where MY problem starts
I formatted the drive and everything
I tell it to get the packages from the cd-rom
device is set to scsi-int/sd@2 (SCSI ID is 2!)
set the path to /macppc/binary/kernel/

and it doesn't work... any ideas?