generally speaking for dmz with private ips:
1. create DMZ
2. create NAT Mapping (DMZ = home for hosts that are reachable from the outside, so you want your external ips translated into private ips - or map ports of your external ip to the private ips)
3. create inbound rules for dmz (here you use as destination the private ips of the dmz hosts)
the default lan to anything rule allows you to access the dmz hosts
if you like to access lan hosts from your dmz (which you dont do generally) you need to create dmz->lan rules too
hope that helps to find more detailed infos