Whew, what a long journey, finaly getting some results.
I uninstalled avr studio, reinstalled winavr, removed the jungo driver, installed the atmel driver from winavr/utils/libusb/bin
Now when typing the command I receive a bunch of infos, and it detects the ATMEGA8 ;))
It gives some errors at the end however.
Here below screenshots from DOS win :
https://picasaweb.google.com/lh/photo/tWwi8s5Mn2s4J__WX5BRBObcuCOFlv5LhEJP-bL9y9M?feat=directlink
https://picasaweb.google.com/lh/photo/YBtR1z19ZTPQITHKjXwfCObcuCOFlv5LhEJP-bL9y9M?feat=directlink