Hi Helen,
I visited Vietnam last Xmas/New Year. It's a lovely country and the people are very friendly. It's a country of contrasts. Just 20 minutes or so outside the bustle of Hanoi you can see people plowing fields/paddies with a wooden plough drawn by a cow.
When I was there the exchange rate was 30,000 Dong to the Pound or 20,000 to the US Dollar. The shops/restaurants are quite happy to accept either Vietnamese Dong or US Dollars.
Some of the people in my Group had anti-malaria tablets, my Travel Clinic advised me to take them, but some didn't.
You will thoroughly enjoy the experience.
Regds
Jim