Medary.com

primarily in how it's being presented by the media.

That's not me saying it, it's coming from respected military historian John Keegan, writing in the U.K.'s Telegraph:

The recent upsurge of violence in Iraq in no way resembles the Tet offensive. At Tet, the Vietnamese new year, the North Vietnamese People's Army simultaneously attacked 40 cities and towns in South Vietnam, using 84,000 troops. Of those, the communists lost 45,000 killed. No such losses have been recorded in Iraq at any place or any time. The Tet offensive proved to be a military disaster for the Vietnamese communists. It left them scarcely able to keep up their long-running, low-level war against the South Vietnamese government and the American army.

Indeed, insofar as Tet was a defeat for the United States and for the South Vietnamese government, it was because the American media decided to represent it as such. It has become a cliché to say that Vietnam was a media war, but so it was. Much of the world media were hostile to American involvement from the start, particularly in France, which had fought and lost its own Vietnam war in 1946-54. The defeat of Dien Bien Phu rankled with the French and there were few who wanted to see the Americans win where they had failed.

It was, however, the American rather than the foreign media who decided on the verdict. The American media had begun by supporting the war. As it dragged on, however, without any end in sight and with the promised military victory constantly postponed, American newspapers and — critically — the evening television programmes began to treat war news as a bad story.

Emphasis mine.

The main difference between Vietnam and Iraq is that with Iraq, the media were never really in support of the war.