If in four years it is still going on, you may very well be correct, but I don't see that happening.
There are a lot more differences between Iraq and Viet Nam. The most obvious is no jungle. The second, there was a long built up by the enemy forces in South Viet Nam before we even arrived there. The infrastructure for guerilla warfare existed. The people have already seen what will happen to them if Saddam (or someone like him) returns to power. Insight that the Viet Cong did not have considering Uncle Ho.
But the real reason it will not happen is because our troops in Iraq have the full support of this administration, and this administration intends to win.