I swim and it is just as hard/cardio as jogging, but easier on the joints. I have been swimming a little over a year now, and I realized the other day that I no longer dread having decided to have both "shopping day" (groceries, etc.) and swimming in the morning on the same day! I am in such better shape!
I have heard that jogging is good for "beating" the crud out, too, so if he has the opportunity, it would probably be really good to swap out, maybe jogging one day, swimming the next.
Oh! If you have any colleges/universites nearby, you could see if they have any programs for the public. That's where I go (indoor pool-only one on our end of the county!- and it also has weights, jogging track, etc.) and it is really inexpensive! I pay between $140 and $180 <i>a year</i>, depending on which program I join.
The only drawback is that when school is out for holidays and between semesters, the campus is closed, but if he likes to jog, that probably won't be a problem for him <img src="i/expressions/face-icon-small-wink.gif" border="0"> .