I want to post a scene over a starfield I created. I have the two files (one named convoy-background.jpg and one as convoy-aa.jpg). I wish to paste convoy-aa over the background without erasing the starfield. Convoy-aa has a black background and convoy-background is, as mentioned above, a starfield. Could someone please tell me how to paste convoy-aa over convoy-background without erasing the starfield?

I'm using Photoshop 6.0.