Hi Timster,
The trick of making a scene look dark is all in the lighting and a little in the camera. What you need to do is over-light your actual subject and drop all of the other lights to about half of what is on your subjects (Two wall flowers and a kid spiking the punch). Next what you will do is go into your camera and raise the iris to expose the subjects perfectly. This gives your camera enough information to be able to process a clean looking picture and also makes the setting look dark. I hope this helps. Let me know if you have any other questions or if I can explain anything else.
Brandon Cammell
http://www.twitter.com/createmarketing
