I stumbled across an extremely easy way to fix the duplicate GUID problem. I believe it is the manual way of what "zac fsg -d" is supposed to do, but doesn't actually do. Hopefully this information will become irrelevant after the next ZCM patch.

I had been banging my head against a wall while trying to image all of our machines because I didn't clear the GUID before I created the original images, and hundreds of machines ended up with identical GUIDs that just wouldn't seem to go away no matter how many ways I imaged the machines or cleared the ISD (Image Safe Data).

Then I stumbled across this file:
C:\Program Files\Novell\ZENworks\config\DeviceGUID (and DeviceGUID.sav)

If you delete "DeviceGUID", and clear the GUID from your ISD, then restart the computer, your machine will import with a brand new GUID every time!

You can also use that method just before creating an image, and any new machines will then generate their own GUID upon first boot.

It would be awesome if ziswin accepted command line switches... then you could script the whole process.