You're correct that the door panel will need to come off first and then you'll need to remove the regulator (sliding cable assembly) out of the door. Chances are a cable attachment is broke or the cable itself is broken/frayed/off track and the entire assembly will need to be replaced. You can buy a 12-17 year old used one that will eventually have the same problem or a new one from IOS for about $140.
You'll be removing all the 10mm bolts on the door face except the 2 or 3 for the door lock actuator. Roll the window down to where you can get a wrench onthe two bolts that attach it to the regulator. It's a knuckle buster if the window is fully up.
Pages BT-9 and BT-9 of your FSM have good instructions for removing the panel and regulator. Good luck.
http://www.nicoclub.com/FSM/Q45/1996_Q45/1996_Q45/