The best way to get the windows to open is to cut the paint film with a knife blade and free the window from the stops and jambs using a thin putty knife, working all around the inside, and outside of the sash. Once the sash is free, it will rais and lower easily. The window may be held in the jambs by a stop molding. This could carefully removed. The following link illustrates this with pictures and even a video. If we are talking about an older double-hung window, this may help.
http://www.easy2.com/cm/easy/diy_ht_index.asp?page_id=35694621#watch