Can't get autoimaging on unregistered wks to work.

I had a bunch of "new" workstations to add to our school network, so I
thought I'd try to reimage them on first boot.

What I have done:
Created the image object in the container.
Set the imaging server policy to place the image on unregistered
workstations.
Ran ziswin -install at the wks.
When the workstation boots via pxe, I get the message "no work to do",
and it exits and boots to the os.
Using the zen imaging boot cd in automatic mode it did work (at least on
most of the new workstations I tried it on.)
The boot cd also worked in manual mode (for both single imaging and
multicasting.)
Should it not work in PXE boot? What am I missing?

(HP Vectra workstations, press F12 to get to network boot.)

No fun having to boot to the cd at each new workstation.

TIA for any ideas,
Art