Verified answer

I know how, but Im not the best teacher so Ill give it a shot.

Things you need:

Tripod

A remote shutter release

A way to fire the flash off camera

Photoshop

A little patience

Ok, set your camera on your tripod and put your remote release on it if its a wired shutter release. This is so the camera remains in the same position throughout the exercise.

Now...you would take a picture of each person individually with the flash only on them. Use a small aperture (larger f-stop number) to kill the ambient light. This makes the flash your only light source and gets a better result.

Then you take all of those pictures into Photoshop and stack them as layers on one image and erase portions to reveal the person/details you want

check this link out: http://www.zarias.com/?p=340

I think this is what you're after. Sorry for being a poor teacher. I communicate better when I have someone to show hands on.

fade2bkacj suggests a good technique for taking tht pix. load them on to your computer, open photoshop, open each of the pix you want included in the final. then click on 'file', select 'new', select 'photomerge panarama'. then basically follow along with photomerge, selecting the pix you have opened and photomerge will combine the pic as it thinks they should be. sometimes the 'perspective' mode gives a better result. save the merged picture as layers (one of the choices you will be given) and you can adjust each pix in its own layer. when you are done, flatten the image and save as jpeg. if you want to save it for future work, save the unflattened image in PSD document.