http://www.somethingweird.com/cart.p...monsters+crash
Check this page out, and then try clicking on the "MONSTERS CRASH THE PAJAMA PARTY" VHS tape. I recommend it. I don't recommend the DVD for the party because it does not have a "play all" option and the tape will at least play continually for 2 hours.
It is packed with horror shorts and two-bit spook show trailers, and the big feature is the title piece, "THE MONSTERS CRASH THE PAJAMA PARTY," an uber-cheesy no budget film originally created to play the spook show circuit with live monster actors lunging out of the darkness to scare the crap out of theatregoers.
Having a suitable party tape is a good start. It will provide weird noises and will help keep people sort of excited. I would also have everyone bob for apples, but that might be a little too wild for some.