The original gray-faced OS X disks delivered with your system are no longer available from Apple. If you really want to reload your software from scratch, you'll need to obtain either the same disks that came with your system or OS X and iLife disks.
If you look for used gray-faced OS X disks, make sure they are for your model Powerbook. You couldn't use, for example, gray-faced disks from an eMac.
It may be easier just to buy OS X and iLife disks. One source for unopened Apple software is http://www.hardcoremac.com , and they do carry older software.