Have one where two pictures are printed: one for their frame and one to be added to a guestbook where guests can paste in their picture and write a message.
Just make sure that it is somewhat monitored so that your guests are enjoying the rest of your party and there isn't a line waiting for pictures to be taken.
Talk to your banquet manager ahead of time so that they are aware of your plans for the photobooth and can recommend an appropriate location for the booth as well.
Check out http://www.rentphotobooths.com/ for pictures and ideas!
Danielle @ PARADISE