Thread: Ab work?

Is it necessary to train abs? I know they get worked during other activities but I was wondering if it is really necessary to work them seperately too?
If so....
What are some very basic ab exercises? I can't seem to get the form of the crunches right (hurts my back and I feel absolutely nothing in my abs).
And are there any exercises that actually flatten the abs (mine kind of stick out) and create more of a waist line?
Oh, and I'm a female incase that makes a difference.

http://www.myfit.ca/exercisedatabase/exercise.asp