in original Vista Theme it's an ARGB Gradient in UI.txt in shellstyle.dll, not an image
There are a lot Shellstyles around that put an BMP in this area
(the problem is, that it blows up the filesize of the shellstyle (i've seen shellstyles with 6MB Filesize
)
But you can also place an opaque image in CommandModule and Previewpane/1/1
(7 UI does it this way) so the gradient ist overlayed with your desired image.
in my last firedance VS i've linked it (in the shellstyle) to a new image section in the MSStyle, so the background image can be set in the msstyle and the shinelayer is still possible.
how this works, is described here
http://vistastylebuilder.com/forum/index.php?topic=215.0 i'm thinking about a tutorial for this special topic..