Hello,

> I have 2 disks on a PMG4 (AGP) at ultra0 and ultra1 and other
> disk runing macosX connetcted to a ata100 pci card.
> 
> I have installed netbsd in ultra1 drive with partition zero and I  
> have ofwboot.xcf in ultra0 drive.
> 
> I have tryed boot ultra0:\ofwboot.xcf ultra1:\netbsd but it gives
> the error: "can't find a default partition open.. device not
> configured.

That's not going to work.
First question - does ofwboot.xcf actually load?

> I read the docs and they say that it is possible to run netbsd in a  
> partition zero installation.

It also says partition zero doesn't work on OpenFirmware 3.x
Besides that, what you're doing doesn't look like the partition zero
method at all.

You will have to pass a partition number to ofwboot.xcf, like
ultra1:3/netbsd if partition 3 happens to contain the kernel.

The boot command you gave will try to load ofwboot.xcf from the first
partition /that OpenFirmware knows how to read/ on ultra0. This
partition isn't necessarily the first one, OF3 understands HFS(+),
iso9660 and FAT. It does NOT understand NetBSD ffs or Apple UFS so you
will have to load ofwboot.xcf from a HFS+ partition but since you
also have MacOS X installed you should have one.

What's known to work is:
- put ofwboot.xcf on your MacOS X partition.
- figure out which partition your netbsd kernel is on ( pdisk or
the MacOS X Disk Utility should tell you ) then use 'boot
hd:ofwboot.xcf ultra1:3/netbsd' ( substitute '3' for the actual
partition number )
Both the kernel and ofwboot.xcf know how to handle Apple UFS partitions
so you can just create your NetBSD partitions in MacOS X, then you'll
be able to mount them on both operating systems.

have fun
Michael