First the microphone didn't work for me, but I found a hint about the
Global settings manager, because in the settings menu I didn't get a microphone.
In the skype call make a right click and go to Global Settings. In the new browser window follow the link How do I get to the Settings Manager
and follow the Website Privacy Settings panel
In the flash which is opening allow imo.im to access the devices.
Now the http://imo.im Skype has also a microphone. My test showed, that
I'm hearing my voice a like I would be Mickey Mouse, but it works and
Save about 600 MB memory for a virtual Windows Installation in Virtualbox.