It's pretty simple first place the Original OS X install disc that came with the computer in the SuperDrive and restart the computer while holding down the Option key. Choose the Install Disc, choose the language and then click the Utilities Menu. Next choose Disk Utilities, select the internal HD on the left pane, click the Format tab in Disk Utility and ensure the format is set to Mac OS Extended (Journaled) and then click format. This will wipe the HD totally clean. Next exit Disk Utility and continue with the install. After OS X is installed and you have tested everything then use the iLife Install disc and install your iLife apps.