If you still have your 8.1 install CD, you can open that up and go to the 'Support' folder.
In there are a bunch of replacement files for the 6.5 program, which will allow it to use a new WIBU key instead of the old Rainbow one. Just overwrite the files in your existing ArchiCAD 6.5 folder, with the new ones.
Additionally, if you are using a single key(ie. not a NET key), you will need to download the WIBU-key installer from Wibu's website, and run it with the 'Uninstal Kernel Extension' option. Then reboot your computer, and 6.5 should work fine.
CAUTION: To run v9 afterward, make sure that Classic is turned off, or it won't let v9 access the Key.
Josh Osborne - Central Innovation
HP Zbook Studio G4 - Windows 10 Pro, Intel i7 7820HQ, 32Gb RAM, Quadro M1200