Q: leopard and Imac g4

You need to use a FireWire DVD drive. Return the one you bought.

(64248)

Does your Mac meet this? Mac OS X 10.5 Leopard installation system requirements

http://support.apple.com/kb/TA24950

Installing Mac OS X 10.5 Leopard

http://support.apple.com/kb/HT1544

Mac OS X 10.5 Leopard Installation and Setup Guide

http://manuals.info.apple.com/en/leopard_install-setup.pdf

After you install the base 10.5, download & install the 10.5.8 combo update at http://support.apple.com/downloads/Mac_OS_X_10_5_8_Combo_Update

The DVD should look like this

A gray DVD from anothjer model Mac won't work.

Caution - Leopard does not support classic mode. So, if you currently open OS 9 apps in classic mode, you won't be able to do this if you upgrade to Leopard.

 Cheers, Tom