I have been searching a lot for free Camtasia alternatives that would allow me to prepare screencasts. Till date I have found three good tools
1. Free Screen Recorder
Pretty decent tool, allows you to save screencast as AVI files. Best option is to download Vista Codec Package from http://www.free-codecs.com/download/Vista_Codec_Package.htm and in the settings choose XVID compression with as least quality as you want. You can record voice too.
2. DebugMode Wink
A much more complicated software, allows you to store captures as SWF files. Lots of options but little bit uneasy to use.
Free and open source. But resource intensive. Good for high end systems.
Another good tool is ZoomIt by SysInternals. It helps you zoom particular portion of screen, would be useful when u want to show something more clearly, during presentations or screencasts. Free download from
More on sysinternals tools, you get awesome little tools at http://technet.microsoft.com/en-us/sysinternals/0e18b180-9b7a-4c49-8120-c47c5a693683.aspx and they are all free. Amazing tools, trust me.