Yes, exercising your abs is important, but mostly for core strength. The most important thing to get visible abs is actually to lose the layer of fat covering them up. It's not that you don't HAVE a 6-pack, it's just that it's partially covered by a layer of fat.
So yeah, all in all - a good diet and cardio is what you wanna do.
Read this:
http://scoobysworkshop.com/6packabs.htm