It's not as hard as it seems when you know how. I worked out how to repair my driver's side internal handle/lock cable linkage. Took a while the first time, but once you've done it once, it's a cinch.
1. On the underside the pull grip on mine is a little hole - put a screwdriver up there and lever off the front of the handle assembly. That will reveal the rest of the handle with two Philips screws. Undo these and pull the grip away.
2. Move the plastic panel that the pull grip was mounted to towards the front of the car and remove it, then do the same with the panel that houses the door handle so it's held on by the cable. Underneath the handle panel is another Philips screw. Remove this. Also disconnect the central locking switch.
3. Undo the two screws at the top of the internal door panel. (One at the front, the other at the back)
4. Carefully place a screwdriver under the rear of the window switch housing. That should be enough to unclip the switch housing. Pull it free and then disconnect all the plugs from the switch.
5. Pull the internal door panel up - it should just lift away - and carefully feed the door handle through the gap for the cable. On mine it did fit though the gap, but only just - you'll have to tilt it about 45 degrees. Also, pull the electic window cables through the hole.
Refitting is (in true Haynes manual fashion) more-or-less the reverse, but watch out for the door lock knob - it's a ***** to get lined up correctly!
Hope that helps...