The latest update of ‘Ice Cream Sandwich” let you take screenshot on your Motorola RAZR XT910 easily.
Press Power Button and and Volume Down button and hold for a while. This will capture your visible screen and save it to your Internal Storage/SD card. Please remember, you have to press those button simultaneously, pressing one before and other later will not make screenshot. The path of the screenshot would be INTERNAL STORAGE/Pictures/Screenshot