How to get Styler to open as default (vs Editor)

I used to be able to edit the Windows Registry to have Styler open as the default program for *.xml/*.dita files.  However, since Windows 2007, the registry is has changed, so I can't figure-out how to do this "hack" anymore.  So, I have to launch Styler first, then open a *.xml/*.dita file.  Has anyone figured out how to set Styler as the default program?  (I'm on Arbortext 6.1 if that makes any difference).

Thanks, Todd