I've put the HD card into that G5 with Mac OSX installed. When going to System Information and PCI cards it reports an error saying that "An error happened while collecting information" (or so). Maybe that card is really broken. :(

On MorphOS I see that it is booting. My USB hub is starting the blue lights and I can reset via the keyboard. So I guess it doesn't crash but there is just nothing on the gfx card output.

Getting the X card later today....