Could the war have been won? And if so, how?
As it was, No. Thats like saying, could Russia have beaten Germany if they stopped at pre-Barbarossa borders. A lot of Anti-Americans use Vietnam to show that America can be defeated. Sure, the whole world could have been defeated by North Vietnam if they never had fear of invasion. There were more rules to the Vietnam war than in a Highschool chess match, it was ludicrious to have even attempted to fight under such duress.
People often compare Russias falter in Afghanistan as "Russia's Vietnam" you can't even begin to compare the two. Russia could invade and did, could conduct war in a mode in which they saw fit and just, as they had no restrictions such as America in Vietnam.
So much has been said of the Viet-Cong that one who has minimal knowledge of the subject would think they single handely whipped the American imperialists. The cold hard fact was that after the large lossess after Tet, the Viet-Cong were a spent force. The NVA, while not as bad off as the VC, were still considered a viable opponent.
The single biggest opponent in America's fight in Vietnam was America. Propaganda was the best weapon North Vietnam possessed, outside of jane fonda(notice no caps, as she desrves none).
I remember watching a special on A&E about Vietnam and a fighter-bomber pilot said "he couldn't believe the stupidity that was involved in conducting that war" he was telling the interviewer about bombing a railway junction in Hanoi, but he couldn't bomb the SAM's that were sitting adjacent to an area deemed off limites. He said it was hard knowing just a quick burst of MG fire would destroy the SAM's, but they were left alone and were probably the same ones that shot him down a few weeks later.