War in Iraq= Vietnam War?

In history we just finished up learning about the Vietnam War.
The Vietnam War was an extremely expensive, extremely dangerous war, that had many casualties. Why did it start? because the US was so afraid of Vietnam becoming Communist, it felt inclined to "protect" it. Well in trying to protect it from Communism, the US ended up turning it to Communism. Many of the South Vietnamese who originally supported Democracy turned toward Communism after seeing time and time again the US soldiers killing civilians because it was so difficult to distinguish civilian from enemy because of the guerrilla warfare techniques. Also, the US sent troops into Vietnam gradually, slowly increasing the amount over time. Many soldiers who fought in the Vietnam War came back with post-dramatic stress disorder, and were not able to live as they used to. It is well known that this war was a complete failure and a mistake.
One would think after attending even a high school history class, that a person would know that the techniques used in the Vietnam War were not effective, yet it seems like the same techniques are being used in Iraq. The US is sending troops over to Iraq very gradually, and are fighting people who are also using guerrilla warfare. Hundreds of soldiers are coming home with Post-Dramatic Stress Disorder. The war has been extremely costly. How can we, as a country, expect this war to be successful? If the Vietnam War was a mistake, then wouldn't this one be viewed as a mistake as well, in only a few years from now?
I don't understand it. Why would anyone use techniques that had already failed in the past? It's like taking a drug that is already known to be fatal. Maybe President Bush was asleep when his history class was learning about the Vietnam War.