Vega bros would be the titest movie ever, if QT made it right after Pulp Fiction. Travolta and Madsen are just too old and fat. They would have to cast younger actors and that would suck because those actors make those characters.
I've read a lot of magazine interviews with QT in the past year since the Kill Bill vol. 1 hype started, QT always says that he won't do a Vega bros movie. Also, he's gonna do his WWII epic (its gonna be long, 3 hrs or even 2 2.5 hr movies), then he wants to do a western. And he's said numerous times that Kill Bill was originally going to be one movie, but split it up because Miramax didn't want to release a long movie, but its more likely they saw an oppurtunity to make double their money. I don't know where you heard it was suppose to be a trilogy, but it seems really unlikely.