Ardesia 0.3 is out! You can use the wiimote whiteboard with Ardesia to annotate on the desktop This is avaivable for Linux and Windows http://code.google.com/p/ardesia/
You can try to build it on Mac following http://code.google.com/p/ardesia/wiki/CompileOnMacosx
You can see some screenshoot on http://code.google.com/p/ardesia/wiki/Screenshot