1: ilife will NOT remain after a CLEAN INSTALL. it will remain after an archive and install or upgrade, but not a clean install. to install it, just install it from your computer's original OS disks. just choose 'install extras' or whatever the options are and you'll get ilife on leopard. it will not be ilife 08 unless that's what came with your mac (or bought it retail).
2: people keep asking because ilife comes with their computers on their OS install disks. what else do you expect them to believe?