GO TO A BIG BOX STORE, (there I said it) and find a pre fabricated pocket door assembly. They come in two styles; Stanley makes a kit that you put together, and another brand available around here, PremDoor, makes a fully assembled unit. Either product will tell you exactly how to frame your wall, but essentially the frame for the pocket door replaces any normal stud framing you would place in that location. You will need to add a framed in header above the door and the pocket, but that's about it.
Be VERY CAREFUL not to penetrate the pocket door cavity with any drywall screws, nails or anything else. Otherwise, when your project is all finished and beautiful, and you go to close the door for the first time, SCRAPE!!!!! Ruined. Ugly. Blech!
Take your time and read the directions carefully. They are actually kind of fun to install.