A BarCamp has been described as an "unconference". A conference where the topics, sessions, speakers are all determined by the people who show up. Sort of like the concept of a Wiki applied to conferences. Another way to think of it is a do-it-yourself conference.
You want to discuss the merits of Social Media? Scribble your topic on a piece of paper, tape it to the "Session Wall" and see who shows up! You'd love to see a demonstration of Google's Android platform? Maybe put up "Sessions Wanted" sheet and list "Android demo" and viola, instant session!
As of this writing, I've attended only one BarCamp. That was enough for me to realize that I want to attend as many as possible. So much so, that I've registered a domain and setup a mailing list to get the conversation moving in the Fox Valley.
In addition to the participants ("campers" if you will) there are many other factors that contribute to a successful BarCamp. Venue, projectors, WiFi, tables, chairs, food/beverage, restrooms, etc, etc. If any interested have leads on these items, or potential sponsors/donors email the mailing list.