You can't use Software update for Flash. There is no redirect to the last version to support PPC Macs.
The last version of Flash for PPC Macs is 10.1. Scroll down for the download link for 10.1:
None of the new versions of Flash are PPC Mac compatible.
Flash Player version 10.1.102.64 is the last version available to PPC Mac users.
See Texas Mac Mans post here for more info:
See the post by Texas Mac Man for the Flash hack for YouTube:
It's sometimes hard to get good advice, especially for PPC Macs.
There are many new(er) users that don't know PPC or don't know the difference between PPC and Intel support.
There is also lots of Voodoo and mis-info out there.
We try and keep that to a minimum here.....
TenFourFox is a web browser; an alternate to Safari.
I don't know that it's necessary for you, and it may be limiting.
From the developer:
If you require using Flash, Java or other plugins, do not use TenFourFox.
Some people like it. I don't use it.
If your issues are limited to Flash support, just stick with Safari and use the hack.