Nice table utalore, gives an impression. But I think it's fictional since most of the troops you mention are already used in Iraq and Afghanistan??
My question then would be what do you mean by hold Tehran? Because I believe some 100.000 troops might perhaps hardly be enough to beat Iran militarily (in conventional terms) so that you can maybe secure/destroy nuclear sites / key military infrastructure. However, with Iraq in my mind, I'm quiet sure this won't be sufficent to stabilize the country or force a regime change.
The Al-Quds as guerillias and their attacks crazyinsane mentioned don't seem of real value in a full scale war to me. The iraqi repuplican guards were demolished in a good week by a highly skilled and technology wise FAR superior force.
I somehow think those Al-Quds and other guerillia special forces are not able to withstand a full scale military onslaught over a longer period.
Where they come into full play (and what's the US' weekness - relativly small number of boots on the ground becuase of a shift to more technology and less soldiers) is the potential following nation building when there are no more frontlines left.
My experience in the army was that light infantry units, and even fairly elite units like Rangers, get badly mauled in a set piece battle where heavy armor is involved. You just have no idea how nasty tanks and other AFV's are until they overun your position and massacre EVERYBODY! At Ft Irwin (National Training Center), our FARP was overun by OPFOR T-72's, and the result was sadly predictable, although one of my friends did "kill" two or three tank commanders by sniping from cover, before they flushed him out and chased him under a road culvert. A T-72 actually stuck the main gun barrel in after him and he was ruled very, very dead by the referee/observers. So, the armament and refueling station for all of our helicopters was gone, and all of the trained personnel killed, for a loss of three tankers on the other side.
Spec ops and light infantry can only do so much against steel and composite armor combined with thermal optics and weapons that can kill you miles away. It makes for great fiction, but the training excersises always end in a slaughter for the grunts.
Of course, Iran is developing a fairly modern armored force, but would have difficulty trying to protect it from dedicated air attack. While fixed in place by air assets, we would ample opportunity to move in additional division level artillery assets and destroy them in detail, which is largly what happened to the bulk of Iraqi armor just outside of Baghdad. It's a bad situation to be caught in, because armies without the level of C cubed capabilities we have, coupled with redundant levels of aerial surveillance and air supremacy, just can't respond effectively in a set piece battle. That is why MOUT guerrilla options are the most promising avenue of resistance for most of our potential adversaries. By fighting in urban terrain, our ranged weapon and air superiorities are largly negated, and we can be engaged with cheap and effective RPG type weapons at close range. additionally, over-reaction on our part creates disproportionate civilian casualties, which also works in the defenders favor.