Hello Manfredo,
If you still don't have the video working try to test if you can run Skype video session. Perhaps, there are some general issues with camera capture.
I have noticed with astonishment that if the PC Host OS is Win XP and PC viewer OS Win 7 Ultimate, in the Host hear what sent by the Viewer.
Could you please elaborate more on this? You mean, you run the Voice and video chat and can hear on the Host side what is being said on the Viewer side?