this is the piece of software that I used to fix this problem on a customers machine.
Go here; http://www.fatcatsoftware.com/iplm/ and download the free version.
now use the Rebuild function to fix the problem. It will creat a new library based on the XML data contained in the old library.
The good thing about this software is that it is non destructive. You do, of course, still have the original on the G5 and you made a copy of the iPhoto database too.
give this software a whirl and let us know how you get on.
Oh yes, I forgot, the rebuild will not recreate albums or slide shows, just the pictures.