I have a US Cellular Mesmerize (Samsung Galaxy S) running gingerbread 2.3.5 and I have not been able to screen capture message threads. When I hold the back button and tap the power button, the screen switches back to the message board. I believe this was done on purpose by the android programmers, but I don't know for sure. I found a work-around. First, go to the message thread. Hold the back button, which will take you to the message board. (If you try to navigate back to the message thread while holding the back button, the screen will flicker back to the message board before a capture can take place.) You must first do a screen capture of the message board. Then, while still holding the back button, you should be able to navigate to the message thread and do a screen capture.
