Hello Frank,
I had exactly the same problems with a Voodoo5 after a hard drive failure. Following lengthy dialogue with Elbox, we finally figured out the problem. It's due to using the wrong versions of the voodoo.card driver and the pci.library.
You should be using voodoo.card v4.23 and pci.library v6.0+
If you run MedConfig, it will tell you what versions of all the relevant files you are using. You must ensure the driver and library are correct version.
Cheers,
JaX
EDIT: The PPC system may use different file versions, I don't remember, but the principle is the same.