If you're not able (or don't prefer) to setup a full server environment yourself on your local system, you should get one of the excellent pre-packaged solutions. For you, MAMP (which is what I and many people use): http://www.lullabot.com/videocast/install_local_web_server_mac_osx
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for a simple Drupal install it is not
But if you would want to use some image handler module like ImageCache, it will be necessary.
If you're not able (or don't
If you're not able (or don't prefer) to setup a full server environment yourself on your local system, you should get one of the excellent pre-packaged solutions. For you, MAMP (which is what I and many people use): http://www.lullabot.com/videocast/install_local_web_server_mac_osx