Thanks to all…
First, the drive will not be used as a media drive in FCP, just to backup files. While the 2 previously created WinXP partitions were not recognized on the G5, going into the Mac Drive Utility was the solution. I was able to format the second partition there, and it seems to have left the PC partition intact.
And Amazon is having a special on MacDrive for $24.99, so I ordered it earlier (there’s also a five day free trial on the MacDrive website).