On a Xantia? You don't need to take the door apart. The strip's held on by mushroom-shaped plastic clips, which pop into the holes in the door. You slide the strip either back or forward to remove it - I can't remember which...
Alternatively you can rip the strip off with brute force and replace all the clips while you're there. I think I paid €1 for five clips from the local stealer when I had to replace the rear driver's side one's on my old Xantia.
