multicasting extremely slow

I am running Netware 6.5sp6, ZEN 7 sp1, HP Procurve 5406 switch. If I send an image to a single target workstation, this 8 gig image will take about 28 minutes. I can send the image individually to multiple (say 5) targets and the entire process takes the same amount of time. Now if I try a multicast session, the session will take about 5 hours. I would like to multicast images to our labs in our schools but this multicasting is way tooooo slow. What should I be looking at to get multicasting to work at a comparable speed to what I see when I send individual images? Thanks for any help.