I rode through Vietnam last year and as Pecha mentioned, you will be jumping in the very deep end. Buy a motorcycle and start practicing because the traffic around the larger cities in Vietnam (Hanoi, Danang, Hue, Saigon) is crazy.
Before my trip I read this statistic: "Vietnam reported 11,500 traffic-related deaths last year, but experts say the actual number could be double that. The World Health Organization says the rate is probably about 20 deaths per 100,000 people, among the world's highest." Be careful and let us know how your trip turns out.