Pretty easy - you will need software that supports 32 bit TGAs though...
All you need to do is open up the panel in your graphics application - and create an alpha channel for it (will vary some depending on package used). After that go to your RGB channel and select by color. The outside of your panel should be all 0,0,0 black - so it should be a sinch to grab it all. Once you get that invert your selection, contract a pixel or so, and switch to the alpha channel. Make all of the selection on the alpha channel white (it should be what is under the image on the panel itself).
Then save it out as a 32 bit TGA. Every app that supports alpha channels I have seen will allow you to do this with no problems at all.
Also, you might want to fether the edges a bit to get a smoother transition. That will vary some depending on 2D package used.