Excellent question. With the setbacks in Iraq, it will be later than sooner.
And I am convinced that Iran was W's ultimate goal. W name Iran as part of the Axis of Evil, and we now have have Iran mostly surrounded.
I figure the nature of Iran, Syria and Lebanon will be quite different two years from now.
Having 120,000 guys in Iraq, standing around getting shot at, at staggering cost, for 3 useless years, has made an Iranian campaign politically difficult to muster. It also doesn't help when you have young men being prosecuted for Iraqi "war crimes" which were anything but. Very few recruits and rightfully so. A real commander in chief would not allow marines to get killed by snipers to avoid obliterating a Mosque (hiding place). He would not allow his best infantry to be on trial for their lives for shooting terrorists. Bush is a decent man, and I trust him, but I think he has fallen prey to some terrible advice.