This is dead easy!

Load up Terminal (Applications -> Accessories -> Terminal) and type in the following:

Code:
cd ~
wget http://fpdownload.macromedia.com/get/flashplayer/current/install_flash_player_9_linux.tar.gz
tar xvfz install_flash_player_9_linux.tar.gz
cd install_flash_player_9_linux
sudo ./flashplayer-installer
Then follow the onscreen instructions, dead easy.