If the audience will have 3D glasses you just need two pictures of an object, from slightly different perspective:
PHOTO1>>
----------------------------------------------------:
BJECT::
PHOTO2>>
and then place the pictures over the top of each other, put a red tint over one photo, and a blue/cyan tint over the other.
Put on your glasses and you should have a 3D image.
Otherwise you would need to animate the image and be very clever with it to get a 3D effect.
There is a gimp tutorial for this, I'll see if I can find it.
EDIT:
Here is the gimp tutorial
http://forum.crystalxp.net/index.php?showt...570&hl=Gimp
You could also achieve this using stereograms, though only some people can see them...
http://www.smart-kit.com/wp-content/upload...gram%20bird.gif
If you go slightly bozz-eyed (Not the best way) so that the swans along the bottom merge together, you should see an image form. It is better if you can unfocus, by looking at a point behind the image, then moving the image in front of you but without focusing on it.
If you can do this you should see two swans on the image, and it is amazin when you see it for the first time.
It is very hard to explain though...
This one may be easier:

It is the circles but they appear with some in front, and some behind. You can see the image was made by having the circles at different positions, and when you go bozz-eyed (or unfocus) on the image you should see the circles stand out, an some "stand back".
It is a very good way of producing 3D, though they are hard to make complex ones, and you can't easily turn an existing image into one. Though I believe there is (or was) software that would take an image and make a stereogram of it.