The window regulator can be replaced but it is not the easiest job. You can purchase Pontiac window regulators for the transport from several online vendors. I got a new one for $20.00 plus shipping.
Start by removing the interior door trim. There are a couple of screws to remove and then just pop it off. You may break one or two of the plastic pegs that hold the trim on but these are cheap to replace.
Lower the window about half way. Then remove the bolts holding the regulator assembly to the door. There should be 6 of these. Then start unplugging the various electrical connectors. Don't forget the speaker wires. Best to unhook the catch at the front of the speaker and hinge it back then remove the wiring connector from the speaker and set the speaker aside. Work the wiring harness off the bottom of the window regulator frame and set out of the way.
Pop the door latch and door lock out of the pivot they ride in. Be careful not to break the plastic tabs that hold the latches in place. I gently pried the bottom tab down and popped the latches out. Pull the latch operating rods loose from the window regulator frame and let them dangle.
The regulator attaches to the window glass with 2 clips that slide over plastic catches glued to the glass. These catches have tabs on the rear edge which must be depressed. Get help as both tabs must be depressed at the same time (use screw drivers to press them down) and slide the clips and slider bracket to the rear to remove it from the glass. Now work the whole assembly out of the door.
Lift the window glass back up and have a helper hold it up while you run three long strips of duct on the outside of the window, up over the door frame and back down to the inside of the window to hold it in place while you complete the rest of the job.
Take the big spring off. It looks intimidating but will not SPRONG apart. When reassembling, hook the outer end of the spring to its tab on the frame and using vice grips grab the center and wind it up enough to go back into the slot in the shaft.
Turn the shaft to allow the regulator arms to be removed. Install the new regulator arms and reattach the spring. Reassemble in the reverse order.
Be sure to get the rear wiindow slider back onto its track so the window will go into the track freely.
This all sounds simple but the frame does not come out or go back in readily and there is an awful lot of fiddling around (cursing) involved in getting it back into place.
Just look at how every thing goes together before you take it apart. Accept that some connectors etc are going to be hard to reach and deal with it. Remember, someone at the Pontiac factory puts dozens of these things in ever day so it must be possible :-)