I copied the official ISO data to /temp/burn and ran

mkisofs -A "NetBSD 2.1 macppc unofficial" -N -L -l -o  
macppc_unofficial.iso -P "Unofficial Unsupported" -p "Unofficial  
Unsupported" -R -r -V "NetBSD macppc 2.1 unofficial" /temp/burn

http://user.dtcc.edu/~ctribo/macppc_unofficial.iso

RMD160 (macppc_unofficial.iso) =  
3093aa3dc5f0c1130ec3d7870baa4757c1662c75
MD5 (macppc_unofficial.iso) = 050e6a07871d62f518686dba17c8c054


I tested it on my Beige G3, sort of.
boot command for me was just boot ide1/@0:0,OFWBOOT.XCF

Things I've noticed so far:

- -allow-lowercase to mkisofs works and ofwboot.xcf loads in  
OpenFirmware, but ofwboot can't find /netbsd.macppc to boot. So we're  
missing something in our parsing or cd9660 operations or OF is  
ignoring case or something. Not really important.

- adding -N to mkisofs to kill the ;1 seems to work fine.

- Tried to start X, system console locked up, could still ping it.  
Hard rebooted, kernel froze at booting at adb0 at obio0 offset  
0x16000 irq 18: , hard reboot again and I'm back with an XFree86.core  
file laying around that says it seg faulted. Apparently telling X to  
use a keyboard driver that doesn't exist makes it seg fault. So I  
fixed my config file and tried again. No devices detected with driver  
= ati. Definitely seem to be missing the mach32/64 driver. Driver =  
vga starts in 4 bit color with 256 k of VRAM and compresses the  
entire screen into a 1/2" tall bar.

(--) PCI:*(0:18:0) ATI Technologies Inc 3D Rage I/II 215GT [Mach64  
GT] rev 154, Mem @
0x82000000/24, I/O @ 0x0400/8
...
(II) Primary Device is: PCI 00:12:0
(II) ATI:  Candidate "Device" section "Card0".
(WW) ATI:  PCI/AGP Mach64 in slot 0:18:0 could not be detected!
(EE) No devices detected.



NetBSD 2.1 (GENERIC) #0: Mon Oct 24 22:58:27 UTC 2005
	builds@works.netbsd.org:/home/builds/ab/netbsd-2-1-RELEASE/macppc/ 
200510241747Z-obj/home/builds/ab/netbsd-2-1-RELEASE/src/sys/arch/ 
macppc/compile/GENERIC
total memory = 256 MB
avail memory = 241 MB
mainbus0 (root)
cpu0 at mainbus0: 750 (Revision 2.2), ID 0 (primary)
cpu0: HID0 8290c0a4<EMCP,ECLK,DOZE,DPM,ICE,DCE,SGE,BTIC,BHT>
cpu0: 271.19 MHz, no-parity 512KB WB L2 cache (PB SRAM) at 2:1 ratio
grackle0 at mainbus0
pci0 at grackle0 bus 0
pci0: i/o space, memory space enabled
pchb0 at pci0 dev 0 function 0
pchb0: Motorola MPC106 "Grackle" Host Bridge (rev. 0x40)
ohci0 at pci0 dev 13 function 0: NEC USB Host Controller (rev. 0x41)
ohci0: interrupting at irq 23
ohci0: OHCI version 1.0
usb0 at ohci0: USB revision 1.0
uhub0 at usb0
uhub0: NEC OHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 3 ports with 3 removable, self powered
ohci1 at pci0 dev 13 function 1: NEC USB Host Controller (rev. 0x41)
ohci1: interrupting at irq 23
ohci1: OHCI version 1.0
usb1 at ohci1: USB revision 1.0
uhub1 at usb1
uhub1: NEC OHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub1: 2 ports with 2 removable, self powered
NEC USB Host Controller (USB serial bus, interface 0x20, revision  
0x02) at pci0 dev 13 function 2 not configured
fwohci0 at pci0 dev 14 function 0: Texas Instruments TSB12LV26 OHCI  
IEEE 1394 Host Controller (rev. 0x00)
fwohci0: interrupting at irq 24
fwohci0: OHCI 1.0, 00:d0:03:56:xx:xx:xx:xx, 400Mb/s, 2048 max_rec, 4  
ir_ctx, 8 it_ctx
obio0 at pci0 dev 16 function 0: addr 0xf3000000
mesh0 at obio0 offset 0x10000 irq 12: 50MHz, SCSI ID 7
scsibus0 at mesh0: 8 targets, 8 luns per target
bm0 at obio0 offset 0x11000 irq 42,33: address 00:05:02:xx:xx:xx
zsc0 at obio0 offset 0x13000: irq 15,16
zstty0 at zsc0 channel 0
zstty1 at zsc0 channel 1
davbus at obio0 offset 0x14000 not configured
swim3 at obio0 offset 0x15000 not configured
nvram0 at obio0 offset 0x60000
wdc0 at obio0 offset 0x20000 irq 13: DMA transfer
atabus0 at wdc0 channel 0
wdc1 at obio0 offset 0x21000 irq 14: DMA transfer
atabus1 at wdc1 channel 0
adb0 at obio0 offset 0x16000 irq 18: 3 targets
aed0 at adb0 addr 0: ADB Event device
akbd0 at adb0 addr 15: adjustable keypad
wskbd0 at akbd0: console keyboard
adb0 addr 7: misc. device (remote control?) (2) unsupported
akbd1 at adb0 addr 2: adjustable keyboard
wskbd at akbd1 not configured
ofb0 at pci0 dev 18 function 0: ATI Technologies 3D Rage I/II
ofb0: 1024 x 768, 8bpp
wsdisplay0 at ofb0 kbdmux 1: console (std, vt100 emulation), using  
wskbd0
wsmux1: connecting to wsdisplay0
fw0 at fwohci0: 00:d0:03:56:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx
scsibus0: waiting 2 seconds for devices to settle...
uhidev0 at uhub1 port 2 configuration 1 interface 0ulpt0 at uhub0  
port 2 configuration 1 interface 0
uhidev0: Microsoft Microsoft IntelliMouseM-. Explorer, rev 2.00/4.24,  
addr 2, iclass 3/1
ulpt0: Hewlett-Packard DeskJet 1220C, rev 1.00/1.00, addr 2, iclass 7/1
uhidev0: 3 report ids
ums0 at uhidev0 reportid 1: 5 buttons and Z dir.
wsmouse1 at ums0 mux 0
uhid0 at uhidev0 reportid 2: input=0, output=0, feature=1
uhid1 at uhidev0 reportid 3: input=1, output=0, feature=1
ulpt0: using uni-directional mode
wd0 at atabus0 drive 0: <xxx>
wd0: drive supports 16-sector PIO transfers, LBA addressing
wd0: 19092 MB, 38792 cyl, 16 head, 63 sec, 512 bytes/sect x 39102336  
sectors
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 5 (Ultra/100)
wd0(wdc0:0:0): using PIO mode 4, DMA mode 2 (using DMA data transfers)
atapibus0 at atabus1: 2 targets
cd0 at atapibus0 drive 0: <MATSHITA CR-589, , GA0W> cdrom removable
cd0: drive supports PIO mode 4, DMA mode 2
cd0(wdc1:0:0): using PIO mode 4, DMA mode 2 (using DMA data transfers)
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs