This video was on http://www.khayma.com (Google cache) , which appears to have been taken down or redirected to a different site. The threat itself was located at http://www.khayma.com/iraqihell/End%2520US.htm (Google cache) and contains a "countdown clock". This cached page also might have some relevant information on it. Anyone out there know enough Arabic to translate these pages?
(Ah... there is a thread on this here... the text for the countdown page apparently says the following:
"In the name of Allah, the all-merciful and compassionate, the countdown for the biggest event, the defeat and collapse of America, the Hubal of this generation. According to the predictions Al-Sayf Al-'Aasim, _____ at most remain until the prediction is fulfilled. God willing, the collapse of America is nigh." Basically, the clock is counting down to Feb. 4th.)
The actual threat was contained in a Windows Media file called 1.wmv (which I haven't found a copy of, as it is like searching for a needle in a haystack...) and reportedly showed a number of possible scenarios, using footage cut from several different movies, such as "Deep Impact". The implied threat was a bomb or giant fireball from the sky covering New York with a radioactive cloud. A storm of radioactive clouds toppling skyscrapers one by one, along with the Statue of Liberty and Brooklyn Bridge being blown to pieces. An explosion on board a charter aircraft that would cause a radioactive cloud to spread over the city.
The administrative contact for the site is apparently Dr. Sami Shaban, a professor with the United Arab Emirates (UAE) University's Dept. of Medical Education in Al-Ain in the UAE. However, it looks like the site may have been used without his knowledge. One possibility is that the threat may be a complex joke by a hacker. This webpage seems to imply this possibility, and it mentions a 3zat Almomen as a possible culprit.
So, basically this appears to be the "big threat" that the US is all amped up about and which is causing flights to be canceled. It could be bluster. It could be a hoax. And, of course, the vague threat of some kind of apocalyptic doomsday always hangs over us... if we let it.