Getting a six pack and putting on muscle means doing 3 things: cardio in some form, strength training (preferably weight training, with some ab exercises), and eating right. And then, you'll be really ripped!
Cardio (running, swimming, rollerblading, etc.) is the single best way to burn fat. Especially doing intense exercise like sprinting will work wonders for pushing yourself to your max, burning lots of calories, and (in the end) burning up fat. Make your cardio as intense as possible.
The strength training is to build muscle. Training with a barbell and/or dumbbells will make you stronger, increase your muscle size, and thoroughly fatigue your body with big lifts (bench press, squat, clean and press, etc.). Don't do small lifts, like calf extensions of bicep curls; they won't have anywhere near the same effect on your body as big, full body lifts.
As for ab exercises, just do 5-10 minutes of them at the end of your workout. You're mostly working to burn off fat so that you can see them. Besides, training them more often than you do the rest of your body is just a recipe for overtraining and breaking your body. Not fun.
For food, eat frequently (5-6 times a day) and count calories. Eating many little meals during the day will speed up your metabolism, and counting calories will keep you slightly calorie deficient- so you will burn fat when you exercise. Check out this 6 Pack Abs Diet info.
I hope this info helps!