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"The Bush Administration has almost certainly not approved the timing of military operations against Iran, and consequently any projection of the probable timing of such operations is neccessarily speculative. The election of Mahmoud Ahmadi-Nejad as Iran's new president would appear to preclude a negotiated resolution of Iran's nuclear program. The success of strikes against Iran's WMD facilities requires both tactical and strategic surprise, so there will not be the sort of public rhetorical buildup in the weeks preceeding hostilities, of the sort that preceeded the invasion of Iraq. To the contrary, the Bush Administration will do everything within its power to deceive Iran's leaders into believing that military action is not imminent."
Here's another timeline, this time of U.S-Iran contracts from 1979 until today.