Insert you’re Mac OS X Install DVD or Installation Disc 1.
Restart the computer and hold down the letter “C” as the computer starts up.
Continue to hold down the letter “C” until you see a grey screen with an Apple and a small spinning gear.
Select your language on the Welcome to the Mac OS X Installer screen and click “Continue”.
Click “Continue” on the following screen.
After reading the Software License Agreement, click “Agree”.
Select the volume to which you are going to install. “Macintosh HD” is the default name.
Click the “Options” button in the bottom corner of the window and select your installation type.
Click “OK” and then “Continue”. You will be presented with a confirmation window at which point you can click “Install” to proceed.