Scott, try to disable Web Acceleration if you are on the HT1100 modem. This should present a different IP to the server your trying to RDP into. I personally have been able to RDP into a friends remote Win 2k3 server, but, he didn't have IP Filtering on... IP Filtering will need to take into account the entire Hughes IP block...
Maybe the mods will have a good idea, or see if an engineer can come up with something.
1: Type or visit http://192.168.0.1/cgi-bin/index.cgi?Command=1
2: Click on Web Acceleration on the left menu.
3: Click on Control
4: Place a Check-mark into the Disable Web Acceleration box, then click Submit.
Let us know if it works for you. Please note that if the modem is power cycled, or reset for any reason what so ever, Web Acceleration will turn back on by default, also please understand that IPv4 is drying up, anyone that has a public IPv4 address is very lucky, because almost everyone is being pushed through CGN now because no one has any addresses left.
Worse comes to worse you can probably "downgrade" to a lower end modem on the business account that does offer a true static address.