I have never run an evil game, but I've played in quite a few, and they were alot of fun for the whole group. Greed and fear are the best motivators. Greed as in, wanting power or money, and fear, as in, have at least a small part of the party declare a pact to control the other parts of the party. A close-nit group of lawful characters can work pretty well too. Revenge is a good motivator for all parties, even good ones, tho evil ones tend to work harder at it, and be more violent. If the most important question you have is how to keep an evil party going, and what kind of adventures should you have them do, well, my answer would be to have the party either form a binding pact, or have at least a powerful minority form a binding pact, that will keep them from betraying eachother and ending the game with dead characters. As for adventures, you should definatly get the party's imput on what they want to do next, and then write the adventure based on that. This is a good tactic for good PCs too, to poll the party for thier next objective.
For the first few adventures, use easy to handle senarios like raiding a caravan or the like, and have them gain an enemy in doing this that can come back to haunt them. Two of the evil games I've played in were started in caravan raids, with seperate DMs that didn't even know eachother, and they were the best evil games I've played in.
Eldorian Antar