The Lord of the Rings Rules variants Yahoo Group has a set for Napoleonics.
On To Waterloo are a set of free wargames rules based on the On To Richmond American Civil War rule set.
Dale the Wargamer offers a set of Napoleonic Campaign Rules using the Risk board game.
Guard du Corps is a set of Napoleonic miniatures rules where 1 casting = 60 combatants and one turn = 15 minutes. Basing is as per Empire.