Hey Fenway,
1st off, your son is going to have a blast. My freshman year playing D1 ball (2004) was so much fun...but it is tough. Our Workouts went something like this in the Fall:
Practice 6x per week, for 2-4 hours on average. The first couple weeks were all about evaluation...we'd have to run 2 miles in 14 minutes or less...pitchers had to do it even faster. We were maxed out in our push-ups, sit-ups, etc. Coaches used this to test each guys strengths. And we did all of the speed agility drills to test speed.
I'm a runner, and I didn't train too hard going in, and I was fine. I wish I would have trained harder, and the coach will definitley notice the guys that do. I wouldn't kill yourself training though, but you'll be warn out before it starts.
Our coach also sent out a workout a couple weeks before the Fall started too.
If you have any other questions, just ask. Best of luck to your son.