text: Video: Purported U.S. Hostage Beheaded BAGHDAD, Iraq - The militant group lead by al-Qaida ally Abu Musab al-Zarqawi posted a gruesome video on a Web site Monday showing the decapitation of a man identified as American civil engineer Eugene Armstrong and said a second hostage - either an American or a Briton - would be killed in 24 hours.    The grisly beheading was the latest killing in a particularly violent month in Iraq, with more than 300 people dead in insurgent attacks and U.S...