Without a current system disk, or one specifically for your iBook, I think you're out of luck, because I suspect that you're going to have to do an archive and install at the very least. The Powerbook disk is unlikely to boot your iBook - machine specific disks rarely work on other models.
(Your next purchase should be an external FW drive to make regular cloned backups - in a situation like this you could simply copy the clone, or boot from the external drive)
Anyway, if you cannot find anyone with a RETAIL OS 10.5 disk to borrow, your best bet might be the genius bar at the nearest Apple store. There are Apple stores in Farmington, Stamford and Danbury. Are you near any of them?
http://www.apple.com/retail/geniusbar/Meanwhile, get someone back in CA to send you that system disk via Priority Mail. Well worth the $4.60!