Have you already installed Ubuntu 7.10 (Gutsy Gibbon) ? If not, you should read this post to know how to install a new Ubuntu Gutsy.
Okey! If Ubuntu Gutsy is available, you can follow the following steps to setup extra packages to play DVD and listen to MP3 music.

What packages you have to install are non-free multimedia codecs known as w32codecs and libdvdcss2

  1. Open your sources.list file in any text editors (in this case, I use gedit editor)
    sudo gedit /etc/apt/sources.list
  2. Add this line to the end of file, then save it and close the text editor
    deb http://packages.medibuntu.org/ gutsy free non-free
    You can use the following command to do both step 1 and 2:
    echo "deb http://packages.medibuntu.org/ gutsy free non-free" | sudo tee -a /etc/apt/sources.list
  3. Add GPG key to your keyring with the following command
    wget -q http://packages.medibuntu.org/medibuntu-key.gpg -O- | sudo apt-key add -
  4. Update your sources
    sudo apt-get update
  5. Install libdvdcss2 package to play encrypted DVDs
    sudo apt-get install libdvdcss2
  6. Install w32codecs used by MPlayer and xine
    sudo apt-get install w32codecs