Motion guide

I have an irregular shape made in Photoshop and I want to use it as a motion guide for a movie clip. How can I import it?
(I tried to do it as a png file in order to preserve transparency but it doesen't behave as a motion guide.)
Thanks.

PS is using Bitmaps, unless you are importing the paths (if you used a path type of shape) and Flash is vector. I am pretty sure the guide relies on a path ( and doesnt see the bitmap as a path.) but you can use the trace bitmap feature of Flash and see if you can get the shapes path that way? Not sure if that is a solution or not.

I think that's a fine solution. It mightnot get the exact edges, but what the hey, it's probably close enough.