Thank you for your replies.
When I try to uninstall Totem, my Synaptic tells me that Gnome will be uninstalled as well, and as I use the Gnome Desktop or Gnome skin/layer (whatever it's called) I didn't proceed. The same happens when I try to uninstall the totem-plugin.
I have also tried to install mplayer, but it makes no differene: Even though I have installed mplayer and the mplayer-plugin, Iceweasel still uses Totem in (trying to) open the videos. I have also tried to edit the Preferences in Iceweasel and to define, that "Movie Player" is to be used instead of any other video player when dealing with for instance .wmv-files.
The videos which is troublesome is in the .wmv-format (as far as I can tell) and was for instance located at http://www.dr.dk/NETTV/Update/2008/11/23/154909.htm
Any ideas as how to proceed?