Help ! Ethernet problem!

Hello !

I have download wireshark for mac os x and I have installed it successfully !
My conection to my lan is via WiFi on my Macbook pro but on my DesktopPC (windows xp ) is via ethernet and I can not capture nothing for the devices that are connectet via ethernet only the wifi conections.
I tried to change the Interface from en1 which is the wifi interface to en0 the ethernet interface but is steel the same …

(sorry about my English )