Disks that are provided with a computer like your G5, will not work for the G4. There are hardware and CPU-specific files that are on that version. Probably also true for the iBook set as well.
Either purchase Leopard to get it up to "latest and greatest" (assuming sufficient RAM and drive space), or locate a 10.4.x Retail copy (not a machine-specific copy), available from many reliable online retailers, or eBay if you're living dangerously.
I don't think your install disks for the G5 will work what you are trying to do. You need to start-up from these G5 install disks (that's probably the "won't work" part in your situation) in order to install.
So here's what I would do: Insert the install disks and follow the prompts. Before anything is installed the installer checks your machine anyway if its compatible, and if it's not you will get an error message stating that the disks are not compatible with your machine.
By the way if you'll get it to work use the "erase and install" option
but DON'T FORGET TO BACK UP IMPORTANT STUFF BEFORE LETTING IT INSTALL.
It will erase everything before installing the new system.
If not compatible it'll let you know (without installing anything)!!!
Also check online auction sites for a retail 10.4 Box for G4 PPC, you can find some great deals.