1) Its best to install VLC-Media Player from squeeze backports repository. Refer to post titled: Debian-6 Installation Notes#2 (#5 - how to update Debian) to add necessary package sources to /etc/apt/sources.list
2) Install VLC-media player:
command: apt-get -t squeeze-backports install vlc
If you installed Debian with CD#1, you might be prompted to "insert Disc labelled 'Debian GNU/Linux 6.0.6 _Squeeze_ - Official i386 CD Binary-1 20120929-15:56' in the drive '/media/cdrom/' and press enter"