Read the entire thread. It is stated and explained before that the OS doesn't have anything todo with it. It depends on what kind of drivers your network card is using.
Sorry, just read it all when I was coming down to this post. Ethereal has a setting to capture packets in promiscuous mode. Did some searching and found this this.
this script not worked ;/
in my pc was installed
WLM 8.1
Messenger Plus 4.7
I installed successfully o script in example (converted to .plsc in winrar, inclued the xniff.ocx), but not appear the contact window that opened me =//