For a discussion of the impact the war in Iraq has had on the economy, here is a discussion at the Washington Post.
Not being an economist, I can't much argue the specific points here. However, one cannot lose sight of the big picture. The war must create some side benefit: better access to oil, improved infrastructure, improved international relations (yeah I know), to have a positive impact on the economy. War per se doesn't do anything for the economy than did going to moon per se. It's the side effects that make the benefit. Otherwise, all we'd have to do to improve the economy would be to pretend we are at war all the time, and just drive our tanks and planes into the ocean (or whatever more ecofriendly alternative occurs to you).