What you need to do is create a "reservation" for the receiver's MAC address on your DHCP server. You specify the ip address you'd like assigned in the reservation so that the receiver will get the same one every time.

If you don't know what the MAC address is, then you can:
- look in the original ARM software - I think it shows the MAC addresses for the receivers that have connected
- look in your DHCP sever logs
- close all your dhcp servers down and power a receiver off and on again - after a few minutes it gives up and shows the info on it's LCD display

Hope this helps
Paul