Install the Debian Multimedia Keyring
downloading it from http://debian-multimedia.org/pool/main/d/debian-multimedia-keyring/debian-multimedia-keyring_2010.12.26_all.deb
Finally update your package-list:
apt-get update
apt-get install gstreamer0.10-plugins-ugly gstreamer0.10-plugins-base gstreamer0.10-plugins-good gstreamer0.10-plugins-bad ffmpeg sox vorbis-tools lame faad w32codecs libdvdcss2 ffmpeg mencoder
Obs: em caso do Debian 64bits substituir o w32codecs por w64codecs.
Flash plugin
http://www.forumdebian.com.br/viewtopic.php?f=3&t=15129&p=67785&hilit=flash#p67785
# apt-get install flashplugin-nonfree