Sorry. I meant to write that this is for Gnome/Nautilus (and KDE/Konqueror too would be nice), and by "system wide" I mean "for all users" because this computer has 20-40 users.
When Nautilus sees a CSV file, it somehow has to decide which application to use to open it. In our case, the default is gedit, but OpenOffice.org would be more useful.
I think the solution is in /usr/share/mime-info/