There are several forms of montages. This is one which overlays two different images. One image is yesterday's PAD which was a 10-shot multiple exposure which can be seen at - http://www.pbase.com/image/96186573 - and the other image is a pink dogwood that I made a short while ago whose original image is at - http://www.pbase.com/ed_k/image/96236113
To me this works because of the complementary color contrast of the two images which - coupled with the fact that warm colors advance toward the viewer - helps the dogwood blossoms pop out from the busy background of the multiple exposure (that's the theory, anyway).
Done with two layers - one for each image - and the top layer at 50% opacity in order to allow the lower image to show through (normal blending). This could have been done in-camera with the D300 except that yeterday's multiple was no longer on the memory card when I made the dogwood image today.
So there you have it - a montage made up of a 10-shot multiple exposure overlaid with a straight image. (I really liked the dogwood & was sorely tempted to make it the PAD, but demonstrating something different won out.)