Cool.  FYI, here is the documentation.  I have looked at it before, but never tried making one.  They are written in mostly HTML, CSS, and Javascript packed into a zip file that has been renamed .gadget:

http://msdn.microsoft.com/en-us/library/bb456468%28VS.85%29.aspx
http://msdn.microsoft.com/en-us/library/dd834142.aspx