To rent a movie kit, which includes a DVD player, a projector, and a sound system and a screen just Google something like "movie projector hire" in your local area and you should get lots of options. We found a local firm to us who hire out all the projectors etc for under £50 a night but obviously this will no doubt vary.
You can make it slightly cheaper by using your own screen (a sheet pulled and stretched tight between two poles does just as well).
All you then need to do is add in the popcorn, candles in jam jars, and maybe even a picnic and you have the whole scene set. The kids will love it (and so will the adults!)