Iran appears likely to reject the offer made by the major powers just yesterday:
President Mahmoud Ahmadinejad said, "Pressure of some Western countries to force Iran to abandon its right will not get a result."
Secretary of State Rice had always expected this, I believe, and her negotiations this week with the major powers was, for her, an exercise in gauging those nations' likely responses once Iran responded unfavorably to the offer. If Iran in fact does formally reject the accord, then the only question is which of the major powers will be the first to betray the resolve shown earlier this week in Vienna. Again, my bet is on the French.
Soon, we will be able to start betting on which American politician will be the first to make a trip to Iran to meet with Ahmadinejad and to express his or her displeasure with the President's belligerence. (Jesse Jackson and Jimmy Carter won't qualify for this bet because pretty much their only purpose on the world stage is to make peace with people who want to kill Americans.)
See this piece by Ross Kaminsky at Real Clear Politics for further discussion of the diplomatic dance with Iran.