Here is the steps I found in androidforums.com. Managed to cached it from the broken link. 1. Search, Download and Install Steamy Window apk.
2. Run the application and tab the Back key.
3. Go to the screen you want to print screen.
4. Tab and hold the Home key.
5. Tab the Steamy Window app.
6. Wipe away all the steam.
7. Tab the Menu key.
8. Save the image.
This tips does not works in Android 2.3.4!