Here's a quick "paste-into" demonstration...

first, make sure your files are RGB (if you want them in colour)

next, select the "magic wand tool" (w) and click somewhere in the solid black area (you can increase the Tolerance to get more of the area and also have Contiguous checked)

then open your second image (this will be what gets pasted into the area you just selected in image 1)

finally, go to EDIT --> PASTE INTO (shift-control-v) and you'll see you can select and move the second image around to get the best possible positioning...

If you have the checkbox selected for "Auto Select Layer", you'll be able to just click right in the image2 and move it directly.

give it a try...

see ya' round
:)
retrocity