Here's how to make a 3D picture viewable with red-blue glasses. For this example we will assume that the left eye has the red filter and the right eye has the blue filter.
Using your digital camera take two pictures from two different spots; place the camera at the same height (use of a tripod highly recommended) and take the first picture of your subject. Now move the camera one or two inches to the right, focus at your subject again and take the second picture. Imagine that you are taking two pictures from the viewpoint of each one of your eyes; the first picture is the left eye, the second picture is the right eye (see picture below).
Open the two pictures in Photoshop. Go to the first picture (the left eye one) open the channels window and click on the Red Channel (Ctrl-1). Select all (Ctrl-A) and copy to clipboard (Ctrl-C). Go to the second picture (right eye), select the red channel (Ctrl-1) and paste the copied image (Ctrl-V). Without changing the selected channel click on the visibility indicator of the RGB channel, so that you can view all channels at the same time while you align them...
Choose the Move Tool (V) and use the arrow keys to align the Red channel with the rest of the channels. Use a "vanishing" point for the alignment - in our example I have used the bottom-left vertex of the octahedron (see picture below). Crop the picture and enjoy!