You will need:
(1) Your digital camera - I used a Canon Ixus 65
(2) An old or broken SLR zoom lens - I picked up a Sigma 28-200mm from the broken lenses box of a camera shop for 5 quid, I think the autofocus didn't work.
(3) some really tiny screwdrivers, these SLR lenses are held together with tiny screws
(4) Luck - plenty of it
(5) Black electrical tape, various tubes, superglue, elastic bands, anything else you can think of to make a mount for the lens.
Step 1: Take the lens apart
You are after the lens element that sits just behind the front lens element. Keep all the other bits for other projects.
Hold it up an look through it, does it appear to show you a nice wide image?
Step 3: Test the lens out
You may need to put your camera in "macro" mode (the mode you use to shoot pictures of close up objects) to get it to focus correctly. Try playing with the zoom options on your camera as well, you may have to play about to find the sweet spot.
You may also need to vary the distance from the front of your camera lens to the fisheye lens.
You are after a nice crisp image but be aware that there may be some blurring and distortion near the edges.