[Inkscape-user] Boolean intersection of bitmap and vector shape?

Is there some way to import a bitmap into Inkscape and then trim the bitmap to match some arbitrarily drawn shape?

I've tried doing a boolean 'intersection' between an imported bitmap and a closed curve object I've created to no avail. Do I have to trace the bitmap first?

Any hints or tips how best to do it would be greatly appreciated.

BTW, I'm experimenting with screencasting and have created a quick Inkscape screencast to try it out: ( http://www.youtube.com/watch?v=PfMDIK4uvV8)