There is actually a chemical that you can put on the windsheilds to mask it off. I'm not sure what its called , but it looks like blue "white-out" . You paint it on the windows, let it dry, then paint over it. After you're done painting it , it just peels off of the windows. Check a well stocked hobby store.
Another thing to do is to remove the window from the model.
I did remove the windshield from the car. The original car the windshield came off of was a green one and the one it is being installed on is black. I needed to paint the bottom of the winshield black. I guess I might need to try the 2 options mentioned on a scrap piece. Thanks guys.
update: finger nail polish and plastic windshields do not mix. Its a good thing I tested it on a scrap piece. heww: And seeing that paint thinner is a stronger substance, I really see no reason in even testing it. Looks like I am gonna have to buy another parts car. :roll: windshield--->:hammer:<---me