Step 1: What You Will Need
1. Plumber's hanger iron. It's sometimes called Plumber's Tape, but don't confuse this with teflon sealing tape. Hanger iron is available at any hardware store in the plumbing section. It is simply a roll of sheet metal that's about 1.5 cm wide, .5 mm thick, and maybe 3 meters long, and it has holes punched into it every cm or so. You will only need about 30 cm of it, but a roll of it can be had for under $3, and it can be used for lots of things.
Electrical tape. This is for padding the metal and covering any sharp edges.
You will need a hammer and a decent-sized set of pliers for bending the hanger iron. The pliers pictured here are Vise-Grip locking pliers, but any set of pliers will do.
Step 2: Measure and Cut Your Hanger Iron.
Unroll the amount of hanger iron you will need. Then, find the hole in the hanger iron nearest the point of your measurement - this will be the weak spot. Bend the hanger iron at this point, back and forth, several times, until it breaks off. There is no need to use any tool to cut the iron.
Step 3: Fold the Hanger Iron Into the Final Shape
2. Use a hammer, as in the second picture, to flatten the fold in the hanger iron, so you end up with a shape shown in picture 3.
3. Add about 3 cm to the thickness of your monitor, and measure that far from each end of the hanger iron (for example, my monitor was 1.5cm thick, so I measured about 4.5 cm from the end).
4. Use pliers to bend each end of the hanger iron forward, again with a 30-degree angle, making an 'M' shape out of it, as shown in the fourth picture. Use the hammer to flatten this out as well, so that you end up with a flat 'M' with a long "nose" in the middle.
5. Use the pliers to bend each outer "leg" of the 'M' at a point 2 cm from the top, bending them forward so they stick straight out at a 90-degree angle, as shown in the fifth picture.
6. Bend the final cm of the hanger iron back down again at a 90-degree angle, as shown in the sixth picture.
7. Finally, grasp the 'M'-shape in the middle with the pliers and bend it upwards, as shown in the last picture. It doesn't have to be a 90-degree angle, but at least 30 degrees should be enough. After this bend, make sure that the "m" shape is flat again, except for where the middle of the 'M' and the two arms are sticking up at 90 degrees.
Step 4: Protect the Edges With Tape
The webcam mount will hang from the top of your monitor by the two perpendicular arms and will rest on the middle of the 'M' shape, so those have to be padded. However, I decided to go all-out and just wrap the entire thing in black tape for that 007, lethal Ninja look. Nobody is going to play around with this thing now.
Step 5: Hang the Mount on Your Screen and Attach Webcam.
I actually have a compact clip-on microphone, and I clip it to the other "ear" of this webcam mount. You may not have a mike like this, but having a second mount point is a good thing for an extra little light or something for better picture results.
Remember, this is made of hanger iron, so it can be bent and shaped however you like to fit odd monitor shapes, and it has holes so that you can screw things into it. It's not really strong enough to support a full-size camcorder, but you can fasten other small things to the top of your screen using this sort of technique. If you need to support something large, you will need some much thicker sheet metal, which will be much harder to cut and bend. A tripod would suit you better in that case.