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I assumed that they would work, but perhaps I did something incorrectly. I downloaded a copy of the XBMC (XBMC-SVN_2008-07-28_rev14439-T3CH.rar) and upon checking the archive I notices that the folder structure was fairly similar. I just copied the files from the 'visualisations' folder in the archive to the 'visualisations' folder in /usr/boxee. Even though the files have the same extension, you can clearly see that they have different MIME types. I uploaded a screenshot below the my folder. The Boxee visualizations have a mime type of "application/x-sharedlib" and the XBMC have a mime type of "application/x-ms-dos-executable".