1. Remove door panels. Also remove the arm rests off the front doors.
2. I took measurements of where the new fabric will be and made 1 pattern for the front doors and 1 pattern for the rear doors. Make the patterns about 1/4 inch bigger than the area you have to put the fabric (You'll actually tuck the new fabric in the door seams).
3. The factory fabric is glued on and tucked into the seam of the door. It's a pain to take off (so I just left it on and applied the neoprene vinyl on top of it). Now the neoprene vinyl is not like regular neoprene (the vinyl is a lot thinner than actual neoprene). If you do use actual neoprene, it may be a little difficult to tuck into the seams with the factory fabric on. You may need remove the factory stuff. I used a heavy duty fabric glue. 3M makes a "Super Duty" spray adhesive that works well on fabrics.
4. Once the patterns were cut, I traced them onto the fabric and cut! Note: Again, make your patterns a little bigger than the area you're trying to cover- you can always trim!
5. Before tucking in the neoprene, I applied the adhesive to the factory fabric and the neoprene. Once the glue set in a little bit, I started tucking in the edges of the neoprene with a thin paint scraper.
6. Once I got all the edges tucked in and secure, I went a head and put the door back together, i.e. the arm rests on the front doors as well as the plastic ring that goes around the door handles.

That's about it. It's pretty straight forward once you get the doors off. Sorry to go off-topic Guido, maybe the Line-X would look killer on the inside door panels!