If you talking about the IP of the Mac you are using, Open System Preferences, Network, Click on Built-In-Ethernet and it will show you the network IP of your computer. Below is a pic. If you mean Internet IP and are behind a router, go to http://www.lawrencegoetz.com/programs/ipinfo/.
That will display your Internet IP. Not really sure what you wanted but those should help.
You can also open Network Utilities in the Utilities folder and it will tell you your IP and much other info.
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