The port for Nha Trang, Vietnam is easily accessible to town. It is possible to walk, but only if you are willing to wear plenty of sunblock and sweat a bit. The heat and humidity is strong in Vietnam, so walking to the center of town is a bit of a chore and can take 30-45 minutes. There will be plenty of motorcycle taxis available just outside of the pier gates, along with regular taxis. My experience is that I walked in both directions and it was tough mainly because of the heart and sun. I wish I would have spent a little money on a taxi. However, if the weather is cool and you have the energy, then go for it.
As far as safety goes, I never felt threatened or unsafe. Parts of the area you will have to walk through are a bit run down and dirty. There are generally people everywhere on the streets and mostly, you'll just be hounded to hire a motor cycle taxi or buy something. There is a more in depth post on Nha Trang, in my blog, as well as many photos on my Flick site. Just click HERE for my other post.