This link goes through removing the inner doors from the doors:
http://www.golfmk6.com/forums/showthread.php?t=5095
Depending on if you have a 2dr or 4dr, the rear doors on the 4dr are almost identical to the fronts but with one less bolt holding them in. If you have a 2dr, I've never worked on one, but this link is the best I could find as far as removing the rear interior cards:
http://forums.vwvortex.com/showthrea...I-GTI-Golf-2Dr
The pictures in that thread are really small but I viewed the source and all of the pictures can be seen here in a larger format:
http://s1263.photobucket.com/user/ts...?sort=3&page=2
As far as removing the door cards from the inner doors, they are plastic welded onto the inner doors and have to be cut/broken/drilled off. This picture shows the plastic welds on a 2dr, the 4dr has less welds per panel, but same type of welds.
disregard the arrows, but the lower circular plastic welds I used a drill to drill out the circular welds, similarly to drilling the head off of a rivet, if you're familiar with that, and the upper clips I used vice grips to squeeze the two halves of the clip together, and used a flathead screwdriver to lift the door card up off of the clip. I can elaborate more if you need me to, but it was just one of those things to me that as long as you take your time and work slowly and think everything through, you shouldn't really break anything, and as far as putting them back in, I just used 5 minute epoxy and made sure to set some weights on the doorcards so that they were seated well. Its not difficult, just requires good attention to details to make sure that the execution is perfect.