I have now tried every trick in the book to get the Radeon X1300 AGP card to show MorphOS install screen. I will give up now, I think.
I used the NVidia card to boot into Open Firmware, then coded NVRAM to boot from CD next time. I then shutdown, swapped the NVidia card for the X1300, hoping it would show up after a successful boot of MorphOS from CD. It did not.
I then used the NVidia card again to get into Open Firmware. I set NVRAM back to standard, and instead tried boot-command, telling the command to boot the boot.img from CD. Then shut down, swapped cards, booted - nothing. Screen stayed black.
I then used the NVidia card again to get into Open Firmware. Instead of creating a boot-command to boot from CD, I created one to boot from USB stick. Swapped cards again - screen stayed black.
It seems that the info that X1300 standard PC card running on G5 is either a myth - or I am still doing something wrong. Any help would be appreciated.
Mac Mini 1.25 GHZ, 1 GB RAM, MorphOS 3.20