The British press reported on this a few months ago, now the NY Times has the entire memo. It's real.
From the NYT:
In the weeks before the United States-led invasion of Iraq, as the United States and Britain pressed for a second United Nations resolution condemning Iraq, President Bush's public ultimatum to Saddam Hussein was blunt: Disarm or face war.Even more fun, Bush was prepared to fake the evidence to provoke a US war with Iraq. Gee, sound familiar?
But behind closed doors, the president was certain that war was inevitable. During a private two-hour meeting in the Oval Office on Jan. 31, 2003, he made clear to Prime Minister Tony Blair of Britain that he was determined to invade Iraq without the second resolution, or even if international arms inspectors failed to find unconventional weapons, said a confidential memo about the meeting written by Mr. Blair's top foreign policy adviser and reviewed by The New York Times.
The memo also shows that the president and the prime minister acknowledged that no unconventional weapons had been found inside Iraq. Faced with the possibility of not finding any before the planned invasion, Mr. Bush talked about several ways to provoke a confrontation, including a proposal to paint a United States surveillance plane in the colors of the United Nations in hopes of drawing fire, or assassinating Mr. Hussein.