Photoshop to Flash

Meow. I’ve got a really big PSD file that I’m working on converting into a flash presentation. The layers consist of masked off bitmaps. The problem is, I’ll rasterize the layer and apply the mask. When I bring it into flash, the area that I THOUGHT that I had trimmed away in photoshop is still there. Not cool.
Does anyone have an idea of how to get my bitmaps to behave?