I really doubt anyone is going to actually act before Iran gets its nukes. Where it goes from there is hard to say...
I believe that this assessment of when Iran will get nukes is far more accurate than the 3-7 years being bantered around by the UN experts and members of Congress. My bet is that Iran will test a weapon by the end of 2007 and possibly before the end of this year in either scenario far before any serious efforts like sanctions will be agreed upon.