I am not 100% sure this works with a regular Zune, but here is the method for a Zune HD to sync on a Mac.
• Download Windows Phone 7 Connector Software
https://www.microsoft.com/en-us/download/details.aspx?id=20993
• Launch the software from Applications, then quit the application immediately.
• Open Terminal and type the following command.
[code defaults write com.microsoft.Windows-Phone-7-Connector ZuneEnabled -bool YES [/code]
• Hit "Enter" and launch the Windows Phone 7 Connector Software again, and it "should" work once you connect your Zune.