For those who are alo interested:
2 min ago I got a mail from Sonnet Tech. and the wrote this:
"B&W G3 or G4 (PCI Graphics) machines, no problem. Panther will work with no problems.
Compatibility for Panther is based on the motherboard inside the machine not the processor inside. So if your motherboard is compatible, Panther will work regardless of the CPU inside. We mention that here:
http://sonnettech.com/news/panther_update.html"
So I can buy Panther and a upgrade -) --> fuuun