The only thing I haven't really mastered playing Rugby 06 is the dummy pass. Still trying to figure out how to do it, just because I want to continue my dominance over my friends...
just pass left then pass right (or vice versa) quickly. If you cant do it in a game try it in the training segment, you should be able to do it just fine
Wait till you actually see the player start to pass the ball before pressing the opposite pass button
According to Gay-Guy, the dummy pass is quite useful for quick acceleration from a standing start, see "quick takeoff" in his post http://www.therugbyforum.com/index.php?showtopic=19427, this is actually quite a good post to improve you skills.