What you need:
1. a head (duh)
2. a webcam
3. Head tracking pointer by IBM

The download is easy, just fill out the form to create an IBM id and press download. You also need to extract the zip folder to any comfortable location.

How to use:
The program itself is very smart and will discover any webcams connected.
To start, connect your webcam and open the head tracker.

It needs quite a lot of light to work well, but not too much, or it won't tell your nose apart from the rest of your over-lighted face.

Tilt your head left and right 3 times and look straight at the center of the screen to let it find your nose position, which it will use to determine where you're looking at. You can repeat this at any time, if it starts tracking incorrectly. The pointer should automatically move to the screen center when it finds your nose shadows.

To move the pointer, gently move your head to look at the place you want it to go.
To click, stare at the same spot for approx. 3 seconds. Turn clicking on first from the Main menu to allow clicking. The menu also has buttons for double-clicking, right-clicking and for dragging and dropping.

You can also open the on-screen keyboard:
Start > All Programs > Accessories > Accessibility > On-screen keyboard

Although it will take some time to get used to, this hands-free alternative can be quite fun if you want a change.