4issquared,
First check the type of LNB..the thing on the end of the arm...undo the screw and pull.....if there are two outputs connect the unused one to your second receiver........if there is only one output you have a really old dish,,,,,,,,,,,anyhow get a dual LNB. DTV LNBs are about twenty bucks.
You can run one or two receivers from the dual LNB 18" dish....three or more is multiswitch land. Used dishes are everywhere........find an installer and get a quote.
Call DTV and see what they want and when they can do it.
EZ job.
Joe