broken mirror effect

i'm looking for some help in designing an effect that i have in mind, but haven't actually seen implemented anywhere.

essentially, what i would like to do is pull two images together so that they make up two halves of the box shape that a standard icon is, and have these two images look like two broken pieces of the same glass piece. much like this, but not as clean. more raggedy along the edges and such.

if i were working with one image, i would just play around with the lasso-tool and break the image apart, but since i'm working with two images, how do i ensure that the "breaks" on both images match each other so that it looks like the two pieces could be pushed back together to make a fitted whole?

any tutorials that might help me create this effect would be greatly appreciated.

thanks, all.

eta: ah. also, if there are any tutorials out there (or advisors) on how to make the edges look like actual broken glass (so, not as flat, but as if the edges had been broken/sliced at an angle and you can see the depth of the glass) that would also help immensely. again, thanks.