We flew over to Vietnam on Japan Airlines. The flight from San Francisco to Tokyo took 12 hours, we had a two hour layover in Narita Airport, outside of Tokyo, then boarded another 747 for Ho Chi Minh City. It was a little cramped for me on the flight over, because I have long legs, but aside from that the flight was great. Japan Airlines had nice food, tasty snacks and drinks, and a good entertainment system. You can watch first-run movies (12 movies), play a video game (10 games), or listen to music (18 stations).
A taxi from the airport to the downtown hotels (the Rex, Continental, and Oscar are all around the same block) costs about $5-$6 US. The taxi drivers will try to get a higher price from you, so you need to bargain with them.
We rode in cyclos, which are like rickshaws, except the driver rides a bike that pushes your seat around. Although the taxi drivers warned us about the dangers in taking a cyclo, we rode in them and never had a problem. The prices vary and you'll need to bargain with them. Its usually cheaper just to take a taxi, but you really get a chance to take in the sights of the area in a cyclo.
Another mode of transportation in Vietnam is the motorbike. We didn't ride motorbikes in Saigon, but we did rent them when we were out in the country and you can usually get a motorbike for about $5 US per day, which means from sunrise to sunset. There are also motorbikes with drivers looking for fares and you can hop on the back of a motorbike - it takes two motorbikes and drivers for a couple. Motorbike drivers seemed to speak English more often than cyclo drivers, so don't overlook them as a way to get around the country.
We made travel arrangements through the Sinh Cafe in Saigon for traveling to Nha Trang and into Cambodia. Sinh Cafes are located in most of the major towns in Vietnam. Not only can you make your travel arrangements, you can have a drink or meal there, as well. We took buses from Saigon to Nha Trang and back and, later, into Cambodia. The buses aren't horribly bad, but they are constantly weaving around cows, motorbikes, bicycles, pedestrians, cars, and trucks on the roads. I got pretty carsick on the buses, for some reason. The buses are also noisy, since the bus driver honks his horn pretty much every inch of the road. If you are young and healthy, take the bus because it will be significantly cheaper than going by plane. You get to see the countryside and meet interesting people while traveling this way. If you are older or your health isn't the best, take an airplane. It costs about $75 US to fly from one end of the country to another, or over into Cambodia, but it only takes 45 minutes, Vietnam Airlines is VERY comfortable, and you'll have the rest of your day to sightsee.
We rode on quite a number of boats during the trip up the Mekong Delta and on to Cambodia. It was interesting and you get to see quite a bit of the country, but it was, at times, harrowing for me. When we crossed the border into Cambodia we had to travel for about 2 hours by speedboat - the kind that had about 4 wooden benches to sit on - and it was just tough. Once we got off of that boat we went by bus into Phnom Penh - a bus with no shocks - but we were so glad to be out of the boat that it didn't seem that bad.
Doug and I rented a motorbike in Nha Trang and one on Phu Quoc Island and we had a great time bopping around that way. Doug is a good motorcycle rider and pretty fearless about taking single trails through the woods.
I was really afraid about traveling before I got to Vietnam, but once we arrived I realized how sweet the people are and I wasn't afraid at all. Lots of people there speak English and a traveler won't have much trouble communicating.