Partitioning inherently wipes out the drive, in my experience. I don't believe you can repartition a drive and retain the contents of any existing partitions. Certainly not with any basic tools... Super Duper or some other utility might be able to do that, though I'm not sure.

The other issue is whether a Mac-formatted drive will let you install anything other than a Mac OS on it.

For me, I have a bunch of extra drives sitting about and the G4 Mirror Door has four drive bays, so I built the Ubuntu on one of the spare drives that had been written to zeros. This way, I don't have to touch my Mac drive or repartition anything to check out Ubuntu.