Sniffing (wireless) traffic is more a network admin than a domain admin thing. Unless one uses a secured end-to-end connection, most traffic is transmitted unencrypted and 'can be seen' on the network. Please remember that even an encrypted wireless lan connection does only encrypt traffic from your network card to the access point.
But being a domain admin will also open up some possibilities since you can install sniffers and probes without asking the user for his permission. You might want to check the legal situation in your country before doing so. Sniffing user traffic is illegal or bound to certain rules in some countries.
