Creating videos of your desktop, including audio track and editing features is not all that difficult. You'll be surprised at how quickly and professionaly you can create 'more than passable' instructional vidoes.

Assuming you have an application or presentation already in place, creating a video of that work is straight forward.

Read the video editing in Ubuntu wiki.
This wiki make reference to both xvidcap and recordmydesktop. See the xvidcap howto for instructions on how to setup xvidcap. Setting up recordmydesktop is even easoer. If recordmydesktop is not already installed on your Ubuntu OS, simply use the Synaptic installer and install gtk-recordmydeskop.

See this exceptional instructional video on using recordmydesktop.
Read these articles on using recordmydesktop and using recordmydesktop part2

If you wish to convert an existing video to another format. see the MEcoder video