Q: I don't have real heavy weights to work with. I reach failure, depending on which muscle I'm working, usually around 20 reps. Does that mean I won't see results very fast?

A: That's correct. If you're trying to burn fat, build muscle, or just gain strength, you want to use heavier weights. Rep range between 6 and 12 to failure should make up the core of your exercises. You can do 20+ rep sets once in a while, but it shouldn't be the majority of your workout. Doing 20+ rep sets will help a beginner make some progress (pretty much any exercise program will work to some degree for a beginner) but in the long run it'll simply increase muscle endurance with ony minimal effect on muscle size, fat burning, or strength.