Unassociate a filetype onder Windows XP
1. Open a command prompt with Administrator privileges by right clicking on the CMD icon and ‘Run as Administrator‘.
2. Type ‘assoc .extension= ’, so if you are trying to unassociate a file type with the extension .rcc, use ‘assoc .rcc= ’ etc…
Use the assoc command without arguments to see the list of all current file associations.
Bronnen: (Ook voor windows 7)
http://www.winhelponline.com/blog/unassociate-file-types-windows-7-vista/
http://www.raymond.cc/blog/how-unassociate-windows-vista-7-file-type/