Adobe seems to have made an about face regarding their support for native 64-bit Linux support for Flash today, and released a new preview Flash plugin named 'Square.' This includes a native 64-bit version for Linux, which I have verified works on my Debian Lenny LTSP server by simply copying libflashplayer.so to /usr/lib/iceweasel/plugins — with sound (which I was never able to figure out with running the 32-bit version with nspluginwrapper and pulseaudio).