How do I erase all data from MacBook OS X 10.5.8 Lepard?

See the following Apple Support article for information on erasing a Mac. Skip step 2 as it only applies to newer Macs. What to do before you sell, give away, or trade in your Mac - Apple Support

After signing out if all those things,,,

 1. Insert the Mac OS X Install disc that came with your computer, then restart the computer while holding the C key.

  2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)

   *Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*

  3. Click the Erase tab.

  4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.

  5. Select your Mac OS X volume.

  6. Highlight the drive, select Partition Tab, then Format type... MacOS Extended Journaled, select the Security Options button, choose Zero Out Data, Erase... after completion do a new install.