I have a 2001 Z3 and I replaced my rear window. I don't want to say its hard to replace because it really just zips in and than you push the fabric down. The hardest part is getting to the window to replace it. You have to sit inside the car and hold it up and try to zip this thing. It can be a real pain in the butt to do. Easier with two people.
What you want to be careful about is, there is a zipper on the window and a zipper on the fabric. If you mess the zipper on the fabric up you are screwed, it makes it so hard to get back together.
Be careful and patient use good light and you should be goood.
Also, this guy on ebay sells them for $150.00 just like the factory ones.
2001 BMW Z3
3.0i straight 6 engine
M badge series
Dinan cold air intake, Dinan software, Dinan High Flow Throttle Body, Dinan stage 2 suspension upgrade, Dinan Strut Tower Brace, 18 inch wheels, and don't forget the fancy pedals.