Is there a bus from Kunming to Hanoi? is there a bus from KM to another city in Vietnam?

I am afraid that there is no direct bus to Hanoi or other cities in Vietnam. You may take a bus to Henei from East Bus Station. The buses depart at 10:00, and 19:30, and the trip takes about 7 hours. The fare is CNY 149 or 147. You can book the ticket by dialing 86-0871-68015801.
After crossing the border, you will reach Lao Cai, Vietnam, where you can take a bus to Hanoi (6 to 7 hours). :)