Though the 64 bit flash player 10 for linux is still a beta version,it works fine on Ubuntu 9.04. Install the 64 bit flash player for Linux is quite easy.
1. Download the 64 bit flash player 10 for Linux beta from here
2. Extract the libflashplayer-10.0.22.87.linux-x86_64.so tar.gz to yourhomefolder/.Mozilla/plugins
Note: .Mozilla is a hided folder,you may press "Ctrl+H" to see it.If you find there isn't a sub-folder "plugins" in the .Mozilla ,you can create this folder by yourself.
3. Restart the Firefox. Done!