iMac 400MHz loses ethernet on 2.6.8

[Dana Sibera <dana@danamania.com>]

I have an imac g3/400 that works well under 2.4.27 - ethernet however  
doesn't come up when I use 2.6.8. I have errors when trying to bring  
eth0 up:

SIOCSIFADDR: No such device
eth0: ERROR while getting interface flags: No such device
SIOCSIFNETMASK: No such device
SIOCSIFBRDADDR: No such device
eth0: ERROR while getting interface flags: No such device
eth0: ERROR while getting interface flags: No such device
Failed to bring up eth0.

dmesg only shows two ethernet related entries.

divert: not allocating divert_blk for non-ethernet device lo
divert: not allocating divert_blk for non-ethernet device sit0

lspci does show it's there, the relevant line shows:

0002:20:0f.0 ffff: Apple Computer Inc. UniNorth GMAC (Sun GEM) (rev ff)

and cat /proc/pci also does, showing:

Bus 32, device  15, function  0:
  Class ffff: Apple Computer Inc. UniNorth GMAC (Sun GEM) (rev 255).
    IRQ 41.
    Master Capable.  Latency=255.  Min Gnt=255.Mac Lat=255.
    Non-Prefetchable 32 bit memory at 0xf5200000 [0xf53fffff].

I was under the impression that the module for these machines (gmac  
ethernet) was compiled into the kernel & should Just Work. Is there  
something really obvious I'm missing here, hopefully a known problem  
with a really simple fix :)

thanks,
dana