Or you can make the background transparent. Save the image as a .gif and close it. Re-open, and set the mode to RGB. Then use the Magic Eraser tool to make the background colour transparent. Then when you import into Flash, you should get a clear background.
The best way is to make your backgorund around your image in Photoshop transparent. Then save as a PNG file. You will still have a box boarder around the image but you will only see what isn’t transparent.
PS. The box around your image will be the same size as the canvis you made it on in PS so be sure to crop as much as you can or it will be hard to move you image around the flash stage.