Just did this the other day after being broken into while in San Francisco.

It's not too hard.

1. Remove outside moulding along bottom of window opening (1 screw on inside of door jam, 3 hidden clips).
2. Lower the door glass all the way.
3. Remove vertical center channel top screw to allow some play.
4. Finesse stationary glass into rubber weatherstrip surround from bottom to top. Use soapy water for lubricant, as necessary.
5. Reattach top screw.
6. Reinstall outer window moulding.

Good luck!

2000 Montero Build Thread