First of all. What are anamorphic 3-D pictures?
Anamorphic pictures are 2 dimensional pictures that, when viewed from a certain angle, appear to be 3 dimensional.
This concept is nothing new, The street artist Julien Beever has been doing it for years.
GreaseTattoo already has a great instructable on doing this technique as well as a ton of great examples of the type of things you can do with this. But there is no explanation on doing this technique in any other programs other than Corel Draw.
So after many hours mucking about with GIMP, then Inkscape, then GIMP again, then photoshop I bring you this instructable.

Step 1: Make a New Document and a Grid

Open up photoshop and make a new document to whatever size you want. I made mine
A4 so it would easily fit my printer paper size.

Now go to Image > Image Size and see how many pixels wide your document is and memorize it.

Now make another new document that is a division of your previously opened document.
An A4 document at 300ppi is 2480 pixels wide so I made my new document 248 pixels square.

Now go to Select > All (Ctrl+A) and then go to Edit > Stroke and select any color and make the width around 2 pixels.

Finally go to Select > Deselect (Ctrl+D) and then to Edit > Define Pattern and call it whatever you want and then close the grid square document (You don't have to save it).

Step 2: Setting Up the Grids

Now open up the main document again and make 2 new layers. (Shift+Ctrl+N)
Select each layer and go to Edit > Fill and select it to use Pattern and select the grid pattern you just made press OK.

Now on one of the layers go to Edit > Transform > Distort and grab the middle top drag thingy (Technical Name please?) down to around 1 third up from the bottom of the document.
Note: The lower you drag it down the lower the viewing angle you will need and vise versa.

Now go to Edit > Transform > Perspective and drag either the left or right top drag things horizontally across towards the centre of the page to just under a third in.

now click on any tool and a dialog box will come up to tell you to apply the transformation, click apply.

If you want, you can now save this picture to use as a template.

Step 3: Placing and Distorting the Picture

Now click on File > Place and select your image and move it and resize it so that the bottom of the picture touches the bottom of the document and it is inside the angled grid.
Once you are happy with the placement click on any tool and then press place, then right click on the layer name and click rasterize layer.

Now Ctrl+Click the angled grid and picture layer to select them both. Then go to
Edit > Transform > Distort. Now click the middle drag thingy and move it to the top of the page.
Then go to Edit > Transform > Perspective and click either the left or right drag thingies and move it outwards until the previously angled grid lines up with the ordinary grid.

Now press any other tool and click apply.
Click the eyes next to the grid layer to vanish them and you are done and ready to print your picture out.

Note: If you are more skilled with photoshop than me you could add shadows for added realism.

Step 4: Trouble Shooting...

My Picture doesn't look 3D, what do I do?!??!

You probably need to use a picture taken or drawn from the correct angle. I found this out after printing out 5 copies of the same coke bottle with adjusted angles...

You also can only get the full 3D effect by using a camera but you can also close one eye to get an idea of what it looks like.

You also need to look at the picture from the correct direction and angle, otherwise you see an elongated and angled (Insert name of what you are using). Believe me, it's the truth.

Help! My picture is fuzzy!

your picture is either very low resolution or has been reduced to a very small size and then blown up to a giant size. To get around this make a double size document. eg. Instead of A4 use A3 in portrait. Photoshop is generally pretty good at enlarging and reducing images with little loss in quality though.