I'm the mother of two girls who were adopted from China and I'm very active with a couple of local international adoption support groups. It is my understanding that there is currently a moratorium on adoptions from Vietnam. If you were already in the process, you could complete the adoption, but new applications aren't being processed. See http://www.adoptvietnam.org/adoption/mou.htm
But things change all the time in international adoption. Contact a few agencies with VN programs and ask them.
As for the big question, "would it help?" I guess I'd ask, would it help who? People who are involved in adoption would counsel that if you are going into adoption with the primary motivation of "saving a child," you are in it for the wrong reason. The thinking is that this will always end up being communicated to the child, and the child will think you expect to be thought of as some sort of savior. Please understand that I'm not saying you are this way--it's just something to think about, and if you present yourself as having this primary motivation, some social workers might have a problem with that.
Adoption is quite complicated, international adoption perhaps even more so. Some social workers are very much against transracial adoptions. They see it as cultural genocide. I know that sounds harsh--it does to me, too. Others are more pragmatic, and realize that while the ideal for the child is to be parented by his/her birthfamily, the second best is to be parented by a family from the child's birth culture, and the third is to be internationally adopted into a good home. Sometimes options 1 and 2 are just not possible.
Nowadays, most people who adopt internationally are very committed to helping their children develop a cultural identity. We have joined our local Chinese community center and take language classes. We consider that we have become a Chinese-American family. It's a lot of work (also a lot of fun), but hopefully it will help our children be more comfortable in their own skin as they grow up.
Sadly, children from many countries are placed for adoption for a variety of reasons, but very, very few are true orphans. Most are abandoned by their birthfamilies for reasons of economics, substance abuse, marital status, remarriage where the new spouse won't accept the other's children, and a host of other reasons.
My feeling is that adoption does help the child in question. It may or may not help the "system" in the foreign country to better help care for the children who remain behind. Some people suggest that if you are really altruistic, you'd do better to just give the money you would spend on an IA to a foreign orphanage or charity. Maybe, but most of us adopt for more complex reasons.
One good place for starting to research IA is the Report on Intercountry Adoption http://www.iccadopt.org/
You might also try to find a local support group and start talking to some of the families. Adoption is a fabulous way to form a family. I thank God every day for the IF that lead me to my daughters. But, it's complicated and there are lots of issues to work through, both when you adoption and throughout your family's growth. I'd be happy to answer any questions you have.