I would not buy an older G5 with the hope that an older, similar version of GB is on it.
Mainly, I would resign myself to keeping those original songs in their original format on the original Mac, generate uncompressed .aiff mixes of them to bring into the new Mac, and use the new Mac to generate new songs.
Beyond that, you could try reconstructing the old files using new sounds, or try and figure out how to transfer the old sounds to the new computer. But personally I wouldn't stress too much over old files.
Thanks Matti, your probably right reg G5 ... and I managed to transfer some of the old sounds onto new mac now. So off to the next challenge ... new equalizer for keybords and vocals as my edirol 20 is not accepted by intel core Macs .... why is all this so not compatible?
Well, if there's a silver lining it's that the software works much better on the intel Macs than the G5s!