The problem is that the processor is not an Intel or AMD and has very little support now, since programmers would have to write and compile their programs specifically for those PowerPC CPUs, which aren't being sold anymore. And there is no way to replace it with an Intel CPU since the architecture and sockets are different.
Since adobe flash player has become so large and complex, it would take a lot of effort to rewrite it for a PowerPC processor, so it is highly unlikely that anyone has taken the time to do it. And flash player is updated so often that you would just be out of date in a few months again.
What you might try doing is downloading the video from youtube (put 'link' in front of the URL (but after the
www.) so
http://www.youtube.com/watch?v=opRg7OHufxQ would become
http://www.linkyoutube.com/watch?v=opRg7OHufxQ and that should let you download it, tho I'm not completely sure on a PowerPC) and then play the video with VLC media player or something. It's a lot of work, but it should smooth things out.
Good luck!
Brijar