The G5 is a PowerMac, right, not a Mac Pro?
When the Disc was wiped, did the Mac Pro make the G5's drive some other Partition sheme than APM?
How to format your disks...
(To Install OSX on an IntelMac the Drive it needs the GUID Partitioning scheme mentioned at the bottom.)
Thanks to Pondini, Formatting, Partitioning, Verifying, and Repairing Disks...
I tried loading Leopard on to the G5 hard drive via my intel mac, but the g5 won't recognize that either.
That would install an Intel version of the OS, not usable on a G5 Powermac.
If the reason you used the Mac Pro to do this is a bad Superdrive in the G5, then use the Mac Pro's Optical.
Put the G5's Install Disc in the Mac Pro, boot the Mac Pro in target mode, boot the G5 holding the Option ir alt key down, choose the Install Disc in the Mac Pro to boot the G5 from.
Format the G5's drive again & use APM Partition Scxheme.