Configuring applications to be triggered when an icon is clicked

[AG]

Hello list

Using Xfce 4.6 (version 4.6.1) on Debian testing/squeeze as single user, 
double clicking an OOo icon (*.odt) triggers something called "Okular".  
I am unable to find the trick of having this default to OOo globally 
rather than having to set it manually for each file, via a right click 
option to "open with ...".

Can someone point me in the direction of how to set this please, or 
would the Xfce4 team consider this a KDE issue?  I am using the KDE4 
libraries as per the most recent testing updates.

Thanks for any suggestions.

AG