If you check out my 'original follow-up' on this Post, use the Pocket Door II link I gave Mel. On that page is a link to The Anatomy of a Pocket Door. If you think of it, they do this all the time.
I'm intrigued that you're intrigued. You must be missing something. You 'build' a header (if necessary) and frame up the door. The door comes w/a 'framed pocket'. Outside of that, you fram as you normally do w/2 x 4s and drywall.