Help please!! I'm trying to install Mac OS X Leopard and the installation window is not loading!?

I clicked on the mac os x leopard dmg file and the installation intro thingy loaded. It told me in order to start the installation, i had to press the restart on and the installation window would automatically show up. I've restarted my macintosh (powerbook G4) and nothings there!! what should I do to make the installation window appear in login window? (this is david.gracieeux also)