I used the King/CPC "Cleared for Takeoff" CD-Rom set for my PPL and scored a 97% on the written. I liked the course well enough that I bought the "Cleared for Approach" set to do my IR prep. That said, any interactive courseware is just a tool. If you're not self-disciplined and self-motivated to sit down and work through a lot of material in a timely fashion, you're better off enrolling in a formal ground school.