Yes, that is indeed a kernel panic. Almost certainly caused by disk damage from the symptoms. sknapp351's suggestion unfortunately will likely fail, fsck is run automatically at bootup anyway and has failed to solve the problem after several boots. Also, I'd advise using fsck_hfs rather than plain fsck. The last time I tried plain fsck, it didn't know a thing about hfs volumes and always reported an hfs volume as unrepairable. Even if nothing was wrong with it.
DiskWarrior would be the best answer. Failing that, if you want to copy files off to the PowerBook, all you need is a FireWire cable. Connect the two computers, and make sure the PowerBook is on. Then boot the G5 while holding down the 'T' key. The G5 will bypass the normal boot process and come up as a FireWire enclosure. In other words, all the G5's drives will appear to the PowerBook as external FireWire drives.
Please note that assuming the G5's HD is indeed damaged, it may not mount for the PowerBook. But you can try DiskFirstAid from the PowerBook on the drive (which will likely fail to fix it), even if it isn't mounted. Or let DiskWarrior do the repair.