if you are still looking for how to make a trim on an object, you should be able to find a few good examples in maya's help file, but here's a quickie. after projecting your curve onto your surface, choose the trim tool, and click on the object you want to trim. it'll turn the object white and where you can trim you'll see a thick white border. click on the part you want to keep, and hit enter.

if there's more to it than that i can't remember... i'm at work without access to maya.