Well, it was not really a convention but I like the way it sound. It was more a gaming day ("VII Jornada De Rol De Invierno De Caballeros De Montevideo") that's organized in winter to gather non-perishable food and/or warm clothing to be donated. You can check about the event here and here (both links are in Spanish).
I wanted to run a short low-level adventure using Labyrinth Lord and after some search I bought "Ruins of Ramat" at DriveThruRPG.com. I thought that a short adventure for 4 to 6 1st level characters with pregen ones to speed things up, would be a good choice for the event. I talked about it with my fellow players of our Google Wave game, and I learned that Rob Conley (Bat in the Attic) uses it at conventions. I knew I was on the right path. Thanks guys for all the tips!
And since I'm a "Knight of Dangerous Quests" of the Labyrinth Lord Society, I'm posting a couple of pics (yes, I want those points!) that document the event.
Thanks to all the guys that joined the game (clockwise): Giancarlo, Pedro, Esteban, Rodrigo, Pablo and Leonel.