Red58 has the right idea. I've removed more than a few windows by prying the inner lip of rubber (if its not very flexible, forget it) soaking it with very soapy water and placing a shim of some sort between the metal and rubber (washers, wooden shims) every few inches to ready the glass to be pushed away. Lots of patience, soapy water and a partner on the outside. Once it starts to move away from the metal start working further away down the weatherstrip, 6-12". Its important that you move as much glass away at a time. Good luck.
