You can follow these steps to install a mac OS on an old Mac book following these steps. Here I assume that you have the actual bootable CD for the OS for installation. 1. Restart the laptop 2. Press Command + R key until it shows recovery mode 3. Open Disk Utilities 4. Select the hard drive and try to partition the drive. For example I have created a partition called Partition1 5. Insert bootable CD and restart the laptop. When option comes choose to boot from the CD. 6. Choose partition1 as the place to install the OS 7. Continue the installation process. 8. Once installation is completed then it might need to restart for further updates. 9. Most of the times a more recent compatible version of the OS might be available. In order to upgrade to the more latest compatible OS follow below steps. 11. Find the latest compatible version of OS. 12. Go to apple support sites and manually download the image and click to install. 13. Follow installation instructions and this would upgrade you