Step 1: Material
A dremmel kit with different bits
Protective glasses and gloves
A beading, wiring kit
This is a very messy project, so I suggest you work outside or in a workshop. Hot pieces of plastic fly away a lot while carving the shapes, so you will REALLY need gloves and glasses.
Also, I noticed that different brands and types of CD's / DVD's react differently to the carving tools. Some of them lost their backing, or separated in two differents layers. Make more pieces than you need and expect some of them not to come out the way you want them to.
Step 2: Choosing and marking images onto the CD's
To choose the perfect shape to make a pendant, think stencil. Choose an image that doesn't have any unattached, loose parts. Unless you are much more skilled than me with the power tools, try to choose one that is not too small or detailed.
I printed my images and cut around them, then stenciled them unto the CD's.