Sorry if you could do this in version 4 as I never tried, but I picked up a license for version 5 professional today and it supports EFI based netbooting in the VM. i was able to netboot a blank VM from our Xserve based netboot server into a Casper netboot image, and image the blank machine. ANd it was very speedy.
Seems like a really cool way to test your images and post configuration scripts, etc, without needing an additional machine. I wouldn't go about building my images in one though ;)
