You can take a screenshot if you open the Android view "devices" (under Window --> Show View --> Other... --> Android --> Devices). Click on the device or emulator you want to take a screen shot of, then click the "Screen Capture" button (it looks like a little picture, and it should be next to a stop sign button). Occasionally the device won't immediately load the picture; sometimes you have to close/reopen the screen capture window.

This is equivalent to taking a picture via DDMS, but you can do it in Eclipse instead of opening another application.