Getting a six pack is easy, all you need to do is lower your bodyfat percentage so that it is visible. Everyone has some degree of abdominal muscles. Working your abdominal muscles through strength training will increase the muscle mass there so that it is also more visible.
Don't forget the diet. If you're eating too much everyday you can do a million crunches every hour and you won't get that six pack. Find an online calorie counter and work out how many calories you need. Cut out the fried food, booze, and anything else useless.
It's all about Cardio and Diet doing stomache crunches alone will not help you need to be fit and have a healthy well balanced diet so the muscles become stronger and more defined
situps my friend, many many situps. Also, try to do as many as you can in a minute, the number will start to get higher over time and you'll be paying so much attention to getting that number higher that over the course of just a couple weeks you won't even notice that you now have a six pack !
Forget ab-specific workouts. Start running or doing some other cardio workout. Abs won't show through if there is fat on top of em =P