Thanks to everyone that is going to reply to my question. I do not have much knowledge but have been using U-verse for over a year in a previous home. This house was already pre-wired by comcast. I had 3 tv's, one desktop computer and a wireless laptop.

I just moved to a new house and got U-verse tv and internet. This is a 2 story home. The telephone box is on one of the sides of the house. There is a coaxial cable coming out of it that is connected to a 3 way splitter. One of the coaxials goes inside the living room that is behind this wall. This coaxial connects to the RG and from the RG there is an ethernet cable to goes to the DVR and the DVR to the tv thru HDMI.

From the splitter under the telephone box there is the other coaxial that hides in the veneer, I guess it goes to the second floor to the master bedroom where there is an STB. The STB connects to the tv thru HDMI. My two computers are wireless and I do not have any problem with it.

This house was pre-wired by comcast.  

Well, I wanted to have another stb accross the hallway from the master bedroom, in the second bedroom, but there was no wire at all goin there. The technician said, it would be $50 to run a wire from outside and the $75 to run the inside wire. I didn't go with it, because he wanted to do outside wiring and it would be very visible, also I didnt want to pay the extra wiring. 

I was wondering if I can do my own wiring. From where do I need to get the wire? Do I need to get the wire from the splitter under the telephone box, replacing the 3-way splitter for a 4-way splitter? or can I put a splitter in the master bedroom before the coaxial connects to the stb and run the wire (coaxial) from there to the other room? The floors are carpet on the second floor, so I was thinking I could hide the wire under the carpet and there is around 30 to 40 feet distance from where I want the other tv.

Thanks for your answers.

Chris

Thanks for the answer. I see this is the correct way to do it.

I went to my old house to check on the wiring. I saw there was a wire coming from the NID to the attic. In the attic this connects to a splitter and divides it in two, one goes to the RG (from the RG ethernet to a tv). The other wire coming from the splitter goes to a second splitter, splits in two. It goes to two other tvs. The installation was made more than a year ago by U-verse technician.

 Also, I checked the wiring in my new home. The wire that comes from the splitter and goes to the second floor actually goes to the attic goes to a splitter, from here one wire goes to the master bedroom and it seems that the other stays in the attic/game room and divided by other splitter. Is this possible? How can I check if there is any signal on these wires?

Thanks for your answer,

Chris.