My basic idea is to have lots of round tables, each with a different board/card game and have a volunteer at each table to fast-teach the rules and objective of each game. We have a K-8 school over 2 campuses (K-5 and then 6-8), so I'd make sure that there is a table for each age group (well, a few for each grade set)...I may split it and do one night for K-4 and one night for 5-8 (the 5th graders will be on the 6-8 campus next year).
If that isn't too confusing, does anyone have ideas to add?