There are a number of no cost options for demos. All of the following create Flash compatible screen capture with audio. There are three different options and licenses. These all work well especially for the price.
Camstudio (Windows) - Camstudio is the GNU/Free Software solution. Personally I am a champion of GNU Solutions. I have used Camstudio and it works well for screen and audio captures.
Wink (Windows/Linux) - Distributed as freeware for personal or business use. I've seen many demos using Wink although I haven't used it yet.
Free (for now)
Jing (Windows/Mac OS X) - Techsmith who is behind Camtasia Studio has launch the Jing Project which is free for now. It is a scaled down version of Camtasia and works well on the Mac.
The old saying is that "You can show someone better than you can tell them!" is so true. With these couple of solutions you can do it at no cost with a quality return.