iPad sync with PowerBook consumes unrecoverable disk space

I have a PowerBook G4 running Mac OS X version 10.5.8 and a new iPad. When syncing the iPad with the PowerBook for the first time, everything went fine, but when the (large) photo library was syncing (from G4 to iPad), the available disk space (about 1+ GB) gradually diminished to the point where an error message was displayed that the startup disk was almost void of free disk space. This occurred long before the sync would complete, so I aborted the sync.

After aborting the sync, the disk space consumed for the sync was not freed, even after reboot. At the UNIX level, I searched for large temporary files that possibly I could delete, but could not find any possible targets. I have not yet tried another sync, which maybe could reset/release the disk space (with disabling the photo sync of course).

Any ideas on how to free the disk space?