Let’s say you’re like me and you purchased the Snow Leopard upgrade but you just have the iLife version that came with your Mac. Well all you have to do in order to install iLife after you upgrade to Snow Leopard is pop in your OS X install disc 1 that came with your Mac and click on the Optional Installs folder. Once there, simply launch the package installer for Install Bundled Software Only. This will install iLife which came with your Mac. You’ll have to insert your OS X Install Disc 2 at some point, but that’s no big deal.
So, after you’ve upgraded your Mac to Snow Leopard using a clean install option, you can use your old OS X install discs to install iLife.