I really can't fathom Iran being the one to initiate a war with the US and/or Israel. If anything, it would far more likely be the other way around, with Iran's alleged nuclear weapons program being the excuse.

Because we are bogged down in Iraq, such a war would be almost totally restricted to a massive bombing campaign. However, unless we nuke them off the map, no amount of conventional bombing is going to bring the Iranian government to its knees.  Yes, it will make them mad, very mad.

It would seem reasonable to expect Iran to retaliate by 1) immediately shutting down all of its oil exports thus immediately removing 4 million barrels per day from the world oil market,  and 2) attack US- and UK-bound tankers going through the Straits of Hormuz with land-based cruise missiles.  Regardless of our air superiority, such an attack would not be very difficult, as those missile launchers are easy to hide in the rugged terrain of the Iranian coast, and a super tanker makes quite a juicy easy target. The sinking of a single super tanker would throw the world oil markets into total panic and cause economic havoc throughout the West.

Thus, an attack on Iran would be folly for the US, but the powers that be are just stupid and twisted enough to try it.

You forgot to mention the 150,000 hostages; I mean troops we have next door in Iraq.  The Shia in Iraq are mostly sitting out of the game and letting the Sunni carry on with the insurgency.  Attacking the Ayatollahs in Iran would tick off the Iraqi Shia to no end.  

Imagine you are the American commander in Iraq.  On a normal, sunny day, you cannot secure the road from the Baghdad Airport to the Green Zone.  Now, your team just attacked Iran and the Iranians are sending, oh, four divisions your way.  It is a straight shot from the border across friendly (for them!) territory.  

Helicopters are useless because the Iranians have shipped in gobs of shoulder fired Surface-to-Air missiles and passed them out like beads at Marti Gras.  Any fixed winged aircraft have to come from out of country because of the same reason (they gotta fly `real slow' on landing approach).  And don't count on the US Navy's help from the Persian Gulf.  Iran has some nasty anti-ship cruise missiles from Russia called SS-N-22, Sunburn.  They fly at Mach 3, got a 320 kg warhead, and no one knows how many Iran has.

Let's not forget fuel.  There may be gigabarrels of the black stuff under your feet, but those pissed off Iraqis are NOT going to let a single fuel truck into your gates.  Aircraft don't fly.  Trucks don't drive.  Armored vehicles don't fight.  Hell, even generators don't work too well without the stuff.  Bye, bye air conditioning, computers, anything else that puts the `modern' Army ahead of the game.

Let us review.  Your forces are spread across the country in either large `Enduring Bases' or their satellite compounds.  Every single person in the most heavily armed patch of dirt on the planet is mad as hell with you.  A nearby country with 63 million people is invading.  You have no air support.  There is no naval support.  The rest of the world is mad at your country.  And you have some 150,000 people depending on you...

Anyone want the job?