In an article about postwar Iraq, the Washington Post notes in passing that
Bush, speaking in a business suit before an audience of 1,400 at a black-tie dinner
Best case is that alfjr.com is blowing smoke: it's just a lie, attempting to get attention or increase its audience among islamists. I think that's the most probable possibility.
Alternatively, the claim could be true. There could be a terrorist attack planned within the next few days.
If attempted, the attack could succeed or fail. No matter which it does, the effect of the attack would be to galvanize American sentiment against the terrorists, (unfairly?) against Iraq, and probably (unfairly) against Arabs.
So we would probably immediately invade Iraq. Which might be what the terrorists want. I can't see that it would be productive in the long run to the terrorists.
I don't really see that it's possible that the attack (if it exists) would be called off. This announcement has certainly already come to the attention of the FBI, who are surely taking it seriously. Making a public announcement days before alleged attacks is like spitting in the FBI's eye. The ten-day limit is indicative: given enough time, the FBI can be expected to turn something up. So the terrorists have to act soon.
Not much more to say. We'll know by March 7th if they're blowing smoke or not.