Help with integrating Internet Cable and Directtv

Mom's house got two cable lines going into the house. And, with her Directv, both of these cable lines are used in order to feed a receiver in the living room and another in the master bedroom.

Now, my mom wants to get Internet Cable. The cable guy showed up this morning and claimed he couldn't install the Internet Cable because both of the two cable lines are already being used by the Directv dish. So, I went to RadioShack and bought a digital quality COAX splitter and tried to split one of the lines from the dish to feed both receivers, but only one receiver will get signal at a time.

Is there anything else I can do? Is there a way to split a directv line? If all else fails, I can call Directv to have them haul their butts here to reinstall the dish. The cable guy claimed the dish guy should have only used one line but is easier to use both lines so... But, I hope I can do this myself. So any ideas will be appreciated.

Your DirecTV lines and "cable" lines should be mutually exclusive in that the dish, if it is feeding two recievers in two different rooms,is a dual LNB with a double run of coax coming out of it to feed the two DirecTV boxes. The cable Internet service, if I am to understand you, is from the cable TV provider, no? If so, there should be in place already a coax feed that comes into the house from the street, whether you have service or not. A DirecTV install should not be using cable company coax cable. Look around the house at the point where cable would normally come into the house from the street. If there was ever cable TV service on the property prior to the dish being installed, there should be a cable terminating inside the house. A competent Cable Internet provider ala Comcast will have a tech who can get a modem on that line and get you up and running. If there is no service coming into the house, the cable TV/Internet provider can very easily bring one in from the street. I would assume others in the neighborhood are using cable for TV and/or Internet. If the dish installer used existing line from the cable company, not only did you not get what you paid for on the install, but also, the cable company might have a beef with the installer. If it is as you say, the dish installer needs to make it right, or, you could play dumb with the cable company and tell them they need to bring the coax in from the street to provide you with high speed Inet. I suspect the cable guy may have been a subcontractor and didn't want to do the work to bring a line from the street.
Hi Slip,

This is a brand new house. There is a line coming from the street to the wall where all the cables go to. And, from there, you got two more cable lines that goes to the rest of the house. However, both of these two lines are currently occupied by the dish.

So, you see the problem is that there are 3 lines coming in, 2 dish and 1 cable, but there are only two lines going to the rest of the house. Or, atleast, this is what the cable guy told me. He said the dish installer just need to split the signal from inside the house , and I tried doing this myself but to no avail... sigh.

The cable is provided by Comcast btw.
You can split a DirecTV coax, but it requires something called a multiswitch; you can't use a normal coax splitter and simply feed two receivers--it has something to do with odd/even transponders and a signal going back from the receiver box to the DirecTV dish.

I'm confused though--it you split one of the DirecTV lines, don't you still need another run of coax?

Theoretically, however, you should be able to use something to multiplex the CATV signal onto one of the coax runs, and then use something to split it off either in the LR or DR. Look at the boxes (SAT-D2?) on the following site (just a quick search on my part, may not be the best place to buy 'em):
Hey Ed,

I just checked out the site and then went to RadioShack to see if they have something similar. The SAT-D2 thingy is called a diplexer. If I am reading this correctly, I will need two of them. First one will combine the CATV and DSS signals from outside the house. Then, second and one will break the signal back up inside the house. Thanks again.
To get internet connection from CATV, all the switches and spliters in the signal path must be bidirectional. I seem to remember those diplexers are not. Before you buy it you might want to double check.
Several of the diplexer options on the link page were, in fact, bidirectional. It would be good to check if you are going to RatShack, however...