I've only done halfs but I don't have a specific workout... I just do my regular workouts (swim, spin, run, boxing, abs, dance, martial arts).
I guess I do multiple workouts concurrently when I have a race coming up but I don't really think too much about it.
I just get on the route, enjoy the scenery, spend several hours thinking about how lucky I am to inhabit my body, smile for the cameras and think about how fabulous the high is when I cross the finish line.... there is nothing like race day.
If I reach my 2009 career goal, I'm going to register for my first full Ironman for 2010. It's wonderful incentive.