Shoutbox

Change the localization (remove the texts in your language file) and take the screenshot you need, no need for photoshopping.

The sub-preferences panel image taken from the resources can then be superimposed over the inner panel to get rid of the options,  buttons, texts and other stuff on the inner panel.

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Also remember that you can not only skin Messenger, but also skin Messenger Plus! itself. So you could make a small temporary "skin" (thus with an empty inner-panel) out of the official layout.

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Or maybe even easier, make your own window with a script using the same images and controls. The exact build-up of images and controls can again be copied from the XML scheme resources, which you can easly get with Plus!'s resource extractor in the skinning section of the Preferences.