I just figured I'd add.. after the 10.2.4 update my ibooks sound was *UCKED up sort of like you where saying.
I asked about it around the net and it seems I was the only one having this problem. My G4 tower updated fine too...
People sugested everything, check the disk, fix permissions, reinstall the update.. nothing worked.
Wound up reinstalling the system.
I hope you have better luck.
Bart