Where to hold it:
Someplace that has a LAN setup. A business (often "Play Land" type businesses offer games and stuff for kids and have networks for games) of some kind is bound to have one, if you can get through the proper channels (ask first!!!). Schools and universities have them usually (got any friends who are students?). Visit a nearby college and maybe get permission there.
Who to invite:
People who want to play the game(s) offered! Don't invite folks who are going to hax0r the network and get you into trouble, but get some fun-luvin' folks who want to have some fun. I don't think you need to charge admission. Usually these affairs are pretty informal..
How to get there? (Walk, bus, get a ride, drive, bicycle, you decide). Pick a place that's close though, unless you like to travel. Surely there's a place close by you that has such a thing.
If all else fails.. buy a bunch of computers or have folks bring there's over and hook 'em all into some hubs. (yeah right, but if you want!)