Aquashrimp, From what i've read about post-1975 Vietnam, was that in the years after the war, the government in the North not only "purged" all of the old SV government from the top, all the way down to teachers in grade schools, they also did in the former Viet Cong allies.
If what I've read is correct, the Northern Government was afraid of a Counter-revolution, which would be spearheaded by many of the former guerillas.
Yes, The genocide of the Pol Pot regime was worse...but there was quite a bit of killing after 1975, in Vietnam.
However, I would point out, that although Vietnam and Iraq are similiar on the outside, they are completely different on the inside. Really, trying to compare the two(other than both resulting in long-term U.S. involvement)is extremely diffucult. Your guess that Iran might Invade is a good one...But they will probably wait until things are favorable. 2 years might be a bit optimistic. However, With our fuel crisis, Not trading with them for 20 years(That would include Iran, as well as any other inclined nation in the region) Would probably be out of the question. We simply could'nt withstand being cut off of that much oil for that long. Especially since it would be fueling the Chinese, N.Koreans, etc. The economic implications are too big.