If you are an screencaster, for sure you know that there are not much options to grab your desktop + microphone at the same time. Perhaps you have tried some java programs, or simply switched back to windows and used a virtual machine. Too complicated!
Hopefully, there is still an opportunity: recordmydesktop+jack. I will not describe how to install jack here, sorry, google is your friend :)
But once you have jack up & running, do the following:
Download sources
$ apt-get source recordmydesktop
Install development dependencies
$ sudo apt-get build-dep