It does work, if the image is small and one looks through it. But for big view the only way to get them to cross (since the eyes can't focus that far) is to go cross-eyed... then the effect is reversed!
you got 2 options first: you get a stereo-dunno-thingie you can lay over them... second: get away from your screen a few steps and try looking through it until both pictures unite in the center (sometimes it helps focussing something far away... difficcult to describe)... then you got a three dimensional pic
its pretty much the same effect you get in those *3D-books* (i really hope you have heard of them) where you get a wavy picture with nothing on it, but "looking through it" you can see an object on it.
Easiest way to do it, get a scrap paper to line up with the divider on the image, and look at the image allowing the scrap to stay between your eyes and between the images. This way each eye only sees part of the image that it is supposed to, your brain will automatically superimpose each side on top of eachother creating psuedo 3d,