An integrated plastic window assembly for an automotive vehicle having molded-in functional features including molded-in guide members (16) to guide a movable panel (14) within or across a plastic fixed panel (12). In one embodiment adapted to an automotive backlite (10), a movable panel slidably resides in guide members molded in the lateral edges of a fixed panel. In another embodiment adapted to a sunroof, the window assembly includes a fixed panel (50) molded with a frame (54) having molded-in guide members (58) in which a movable panel (52) slidably resides.