The Washington Post had an article about this. And I found the full Arabic text of this letter (ostensibly from Al-Qa`idah leader, `Atiyyah, in Bin Laden's command to Abu Mus`ab Zarqawi) on the website of the Center for Combating Terrorism at West Point. I don't have time to study it or examine it carefully (I still have 100 pages of Bob Woodward's new book left), but having read it fast certain things are suspicious. Why, first, would Al-Qa`idah commander identify HIS LOCATION in Waziristan in a written letter sent to Iraq? And would Al-Qa`idah's letter not be more religiously phrased?
PS: I still have not read it carefully, but why would the writer (when referring to Dhawahiri's letter) only refer to it being published by "the Americans"? Al-Qa`idah would surely add adjectives.