Ok, with DTV you need a "home run" from the dish to each receiver, it can't be split, that being said.
If you have a single LNB dish, you will need to pull off the "LNB" and see if it has 2 outputs (2 Coax connectors) if it does then run a line from the second output to your receiver and you will be set. If it only has one output you will need to buy one with two (LMK if you need one and I'll see what I can get pricewise).
If you have a 2 LNB dish you should have a multi-switch somewhere with 4 outputs on it, again, run a line from one of the other outputs to your receiver.
If you have a 3 LNB dish (seperate LNBs), again, there will be a multi-swith.
If you have a 3 LNB dish (PhaseIII, the 3 are combined), there will be 4 outputs on the LNB itself, again, run a line from one of the other outputs to your receiver.
PM me if you have any ???s
WTT