I posted a very long message on this topic within the week at
http://groups.yahoo.com/group/bmw318ti I'm a wordy MF so it ain't short but I'll try to drop it here and see if it fits. My findings are as a first-timer who thought the window system sucked. There are lots of FAQs and tips on this and other sites that helped me. These are my additions to those:
First: When removing the door panel DON"T pry out the mirror switch with a screwdriver stuck between it and the door handle. Pull off the "joystick" button and pull from the slots inside the mirror switch housing without touching and damaging the fragile handle. Mine already had some damage so I was adamant there had to be a better way. This is only a problem on the ti with its unique gummi door handles.
Second: You'll need four M6x10mm bolts, nuts, and wave washers to replace the rivets that hold the original regulator in place. Install the top bolt from inside the door-shell cavity (nut on the outside) as clearances are quite tight to the regulator arm at that position. I found drilling out the rivets a royal pain. I even dragged out my compressor and my Snap-On air drill. But every rivet started spinning before I could get either the center drilled out completely or the head drilled flat. I ended up using a chisel and hammer to remove what was left. (Thought about the die-grinder but didn't want to litter the door with even smaller metal shavings.)
Third: There is supposed to be a fuzzy rubber window-channel liner at both the front and the back. Mine was missing the one at the rear. It's a $9 part that one dealer had in stock, which is always telling. BMW calls it a "window guide rail", p/n 51 32 1 960 413.
Fourth: Check for damage to the window tracks inside the door and for easy movement of the plastic slides in the tracks mounted to the glass. Best I can tell from the condition of my door, the slides had let loose at the ball socket and the regulator bound-up under the slide track, compressing and distorting the aluminum track making movement of the plastic slides very tight. Apparently the window went off track and bent the rear guide rail mounted inside the door, too, compressing that channel and distorting it so badly the window could do nothing but bind coming down, popping the clips again. This can also happen if the window is installed and operated when not properly seated in the front track. So check carefully to be sure the window is properly seated in the guide tracks and inside the rubber linings. With the regulator disconnected the glass should slide easily and smoothly through the tracks. If that's not the case, check the rear track for damage. Mine had apparently been this way for some time as the glass had worn a groove in the steel track with the rubber weatherstripping missing in action. All I can figure is that someone was in the door replacing the clips and threw out the rear track liner after not being able to reinstall it into the distorted track. The inside of the door cavity was littered with "hair-clips" from the plastic slides. The rear track is removed with one bolt accessed through the round rubber plug behind the door panel and the track slips underneath the upper window channel at the top of the door. I simply removed mine and peened it back into shape. Others have seen the welds broken and just replaced the track. Either way, make sure the glass slides smoothly before reconnecting the regulator. I probably could have gotten away with straightening my bent regulator arm rather than replacing the regulator once I figured out what caused the problem in the first place, but at $70 and since I had already drilled-out the rivets by that time. . . . .
Fifth: When snapping the ball connections of the regulator arms into the nylon slides, note that the rearward ball is longer than the front and will have more space between the slide and the arm even when installed properly. Conversely, the front ball is short and may look like it is all the way in the slide when compared to the rear one, but it is not. Use a large pliers to snap the front ball all the way into the slide and THEN insert the hair-clip keeper with a needle-nose plier. Many problems in these regulators seem to come from the front ball not being properly seated in the slide.
Sixth: Before you put the door panel back together, check the operation of the regulator while you can see it....slowly and a little bit at a time. The first time you hit full-closed position the motor may automatically drop down an inch or two and initialize itself to work properly the very next time. Don't do as I did and spend an hour trying to diagnose and fix the horrible noise caused by sloppy tolerances in the regulator when first coming off the full-closed position! It is apparently normal and will be rendered inaudible once the door lining is reinstalled. Have faith, you didn't do anything wrong!
I hope this helps.
-Phil