No way
There is no way to "get around" it, as has been stated many times Adobe stopped releasing flash for macs with 10.1. Newer versions will not work on PPC macs like your Powerbook. There is a hack out there (search for flash for facebook ppc macs),it is a hacked 10.1 flash that "looks" like 11.1. It will prevent facebook and a few other sites balking at your old flash. Its probably not the safest thing ever, but it will work. For now.
Your best bet is to move on and discover ways around the evil that is flash, there are TONS of them. I will list but a few:
In tenfourfox: flashvideoreplacer and downloadhelper extensions, then you can play flv or mp4 files outside a browser in VLC, quicktime etc. There is also Quicktime enabler, numerous greasemonkey scripts....
In safari and omniweb and icab: Install Greasekit (involves installing a SIMBL file as before), then viewtube and other greasemonkey scripts, replaces flash with quicktime, works very well on my ibook
mactubes: Hands down the best method for youtube on older macs.
mintube: Is similar to mactubes, but mac owners have to pay. Linux users do not.
hope that helps