Hi everyone,
Knez from the MacDomain.org forums actually made a fantastic discovery. I don't know if anyone heard about this before. I had not, so that's why I'm sharing this with you.
What am I about? Well, since the last Flash version for OS 9 by Adobe was version 7 and most Websites (including YouTube) ultimately dropped support for those earlier versions, it was not possible to e.g watch YouTube videos anymore.
Knez now took our good old friend ResEdit out of the box and opened the Flash 7 Plugin with it. There is a folder names "vers" where he simply changed the version number from 7 to 9. Now, believe it or not, he saved and restarted and ..tada! Flash works again! 
(I've been watching Youtube videos in good quality now. Streams better than in OSX Tiger for me on my PowerMac Dual 1 Ghz. Not perfect, but a great workaround for those of us using OS 9 regularly... Kudos to Knez 

