Note: Before installing Mac OS X 10.5 (no matter how you will install it), check the Mac OS X 10.5 system requirements.
Note: If you already have Leopard installed and have created a Time Machine backup on a different disk, you can simply restore that backup after erasing your disk and installing Leopard. You will not need the rest of this article in this case.
You should make sure you know the following before performing an Erase and Install installation of Mac OS X 10.5:
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- Your Internet service provider (ISP) information, such as their name, phone numbers for dial-up access, and support website 

- Your Internet connection type (for example, if you use dial-up or DSL/cable/broadband, if you use PPPoE, and so forth) 

- Any router, wireless router, or AirPort base station access passwords 

- Your email service provider (if different from your ISP) 

- Your email address and password 

- Your type of email account (for example, .Mac, POP, or IMAP) 

Tip: Passwords and other personal information should be kept in a safe and secure place.
Check out the Mac OS X 10.5 Leopard Before You Install guide for more information.