Mathematica Knowledge Base : Installing a Mathematica 8 Network Client License on Mac OS X

Quit any previous installations of Mathematica that are running on your machine.
Insert the DVD or double-click the .dmg file. A new window appears on your screen.
Drag the Mathematica 8 icon to the Applications folder to install.
Double-click the MathematicaExtras.pkg icon to install the Browser Plugin and Spotlight Plugin.
The Install Mathematica Extras dialog appears. Click Continue.
To perform a standard installation, click Install.
After the files are copied to your hard drive, close the Install Mathematica Extras dialog and double-click the Mathematica icon on your hard drive. Mathematica will start.
The Wolfram Product Activation dialog appears on your screen. Click Other ways to activate.
From the activation method dialog, select Connect to a Network License Server.
Enter the name or IP address of the server on which MathLM is running and click Activate.