Hook up your existing electronics. Connect your laptop to a projector and some small speakers, or your DVD player to a projector and amplified speakers, and plug each item into a power strip with a surge protector. For safety, run extension cords from an outdoor outlet with a ground-fault circuit interrupter.
Improve a screen. Hanging a white bedsheet against the wall is the cheapest substitute for a screen. Or mount a 4- by 8-foot sheet of foam-core board from an art store.
Rent a theater. You can rent a screen, amplifier, projector, and speakers from some electronics stores and companies like funflicks.com (from $299).