I remember there is a way to access a list of all the file associations so you can change them etc. easily (without going to the files of that type and changing it there).
Do you know how to access that list?
Control Panel -> Programs -> Default Programs -> There you should find your setting. It is there in Windows 7, according to my knowledge it is there in Windows Vista as well.
There's also the ASSOC command line command
C:\Users\super>assoc /?
Displays or modifies file extension associations
ASSOC [.ext[=[fileType]]]
.ext Specifies the file extension to associate the file type with
fileType Specifies the file type to associate with the file extension
Type ASSOC without parameters to display the current file associations.
If ASSOC is invoked with just a file extension, it displays the current
file association for that file extension. Specify nothing for the file
type and the command will delete the association for the file extension.