Running Leopard you can't. What you have is as far as it will go.
Leopard was the last build Mac released that was a "Universal Binary". In other words, it would run on PowerPC or Intel Processors. Once Snow Leopard was released, Adobe stopped deveopment on Universal binary builds of Flash Player.
I know it seems like just another "money grab" by Apple and Adobe trying to force everyone to buy a new Operating System, but the entire industry has moved away from the old Apple architecture and software for it.