Renting a car (jeep) on Aruba is a great idea. Suggest that you drive through the new National Park and to Baby beach (where the locals go). If you can't get a jeep, any car will get you around the very interesting island of Aruba.
I pre-booked our car through Avis or one of the majors, and the car was ready for me. Remember though that some of these cars will look a little beat up but don't hassle it.
Have a great time.