Change Default file app to another app when double clicked in explorer

Hi Everyone, I've searched the forms and ran into a road block i think due to not really knowing what its called I'm searching for. Here is a simple explanation. I would like to add a button on my form that if selected will change the default application that a certain file type opens with.

I would like to change say all .txt files to open in Microsoft Word. Then if the user selects the button again, it checks what is currently default for .txt and changes it to the opposite. (Either Word or Notepad).
Note: The files being opened will not be through my program, they could be double clicked in windows explorer.

Hope this makes sense, a little help getting me in the right direction would be much appreciated.

Thanks for any help!!

Cheers,

Mark

should get you started: http://www.codeproject.com/KB/vb/VBFileAssociation.aspx