Just like "start", you have to define "end" better. Do you mean:

- Saddam Hussein is killed / captured / exiled?

- Iraqi troops (with or without their leadership) surrender en masse?

- An American-imposed administrator is "formally" declared the leader of Iraq?

- Iraqi oil production capacity reaches at least 80% of its pre-war / pre-devastation value?

- G.W. Bush declares the war ended?


It's important to note that any and all of these things can occur independently from each other.