Later versions of OF don't seem to be able to boot off raw disk
partitions. You'll need to boot ofwboot.elf off either the network, or
an HFS/DOS/ISO9660 partition, and have it boot netbsd for you.

So, something like

    boot enet:0 ide0/disk@0:0

Or

    boot /path/to/HFS/partition:#,ofwboot.elf ide0/disk@0:0

(you don't need the /netbsd. ofwboot.elf knows that much.)

-- Dan