Changing ZenImage NIC Speeds??

We are running Netware 6.5 sp5 servers with Zen 7. 95% of our switches
are hard coded for 100/full. We have been using ZenImage with the PXE
boot option and just letting it run, but have to change the switch ports
to auto when ever we run an image. What do I need to do to change the NIC
speeds so when we do a PXE boot it forces 100/full? I have see several
TID's on this, but all seem confusing.