If we are directly involved, it will be more like Clinton's air war on Serbia -- no boots on the ground.
The people of Iran are fairly pro western but very nationalistic and would likely turn on us pretty quickly.
As it is I worry that we can't keep up support for a decades long war on terror as it is. I fear that a lot more people in the USA and Europe will have to die before there's a serious effort to crush islamic terrorism once and for all and it will require fighting and occupation forces on the scale of WWII across the islamic world.