Insert the OS X 10.5 Leopard DVD into your Mac.To install OS X Leopard 10.5 follow these steps: For a complete install you’ll need at least an 8gb Flash drive or a larger external USB Hard Drive. In fact it is almost the exact same experience you had when installing the device on your Mac originally. Installing OS X Leopard on a USB Flash Drive is much easier than expected. If either of these sound like you, you may find it handy to have a back up OS X 10.5 Leopard install that you can boot to and make adjustments to your system.
On the other hand, you may have installed the latest updates to OS X and various programs just stopped working. If you’re one of those people that continually adjust system settings, make changes in terminal, and try new and experimental software then you’ve probably done something in the past to your OS X installation that has compromised performance or made things stop working completely. Update: You can now find instructions on how to install OS X Snow Leopard from a USB Drive at Maciverse. Install & Boot OS X Leopard from a USB Flash Drive
