craig
if you can intercept the cabling from the dish to the receiver locations (if they are routed thru an attic)then you can install as many receivers as you want. A device called a multi-switch will distribute the dish signal to as many locations as there are outputs of the multi-switch (there are multi-switches available with 4 or 8 or even 16 outputs). The multiswitch is inserted into the system between the dish and any receivers (if your dish leads are routed thru an attic, they can be cut, terminated and the multi-switch inserted). older multi-switches even have an antenna input to combine off-air and dish signals on the same cable.
If you have a new rca HD dish, it comes with a 4-way multi-switch in the box (of course you need 4 coaxs between the multi-switch and the dish itself). This multiswitch does not have an antenna input.