The discs are machine specific meaning the install disc that came with your iMac won't work on the iBook.
- Mac computer with an Intel, PowerPC G5, or PowerPC G4 (867MHz or faster) processor
- 512MB of memory
- DVD drive for installation
- 9GB of available disk space
- Some features require a compatible Internet service provider; fees may apply.
v10.5 Leopard can be purchased from Amazon.
Go here > http://www.apple.com/support/leopard/
Then click: Contact Apple Support
If they don't sell the Leopard disc anymore, they may have some suggestions.
Yes, if it has the requirements.
Leopard System requirements
You must have a Macintosh computer with:
- an Intel processor or a PowerPC G4 (867 MHz or faster) or G5 processor
- a DVD drive >built-in FireWire
- at least 512 MB of RAM (additional RAM is recommended for development purposes)
- a built-in display or a display connected to an Apple-supplied video card supported by your computer
- at least 9 GB of disk space available, or 12 GB of disk space if you install the developer tools
If you have another computer's installer discs they cannot be used on a different computer. You can buy a retail copy of Leopard on eBay or Amazon that will work on both PPC and Intel Macs.