Kenny Ker recently posted a tool that generates window screen grabs with JUST the window and none of the background for the window

Getting ‘clean’ images of these windows can be hard if the background does not match whatever color you will be rendering the image onto. Inevitably you need to position the window over a white background before pressing the PrtScn key. This is just a pain. To solve this problem and just generally make it far easier and simpler to create a ‘clipping’ of a window I wrote the Window Clippings application.

Here is an example of an Alt+PrtScn of a Windows Media Player skin:

And here are the results of using Window Clippings. In this case I chose to produce a JPEG with a red background.

 

 

Great work Kenny!  Find the download and a lot more information on his blog: http://weblogs.asp.net/kennykerr/archive/2005/09/30/426280.aspx