Open up System Preferences and go to the Network Pane. Select your method of connection (ie Airport, Ethernet, etc.) and the MAC address for your Mac should be listed near the bottom of the pane.
Open up System Preferences and go to the Network Pane. Select your method of connection (ie Airport, Ethernet, etc.) and the MAC address for your Mac should be listed near the bottom of the pane.
Note that it isn't called a MAC address in the prefs, it is referred to as "Ethernet ID" or "Airport ID" or similar, which can be a little confusing. For Ethernet connections, click on the Ethernet tab in the Network preferences, for Airport connections, click on the Airport tab.