The local currency in Vietnam is Vietnam Dong ( VND ). At the time of writing, 1 USD is around 15,000 VND. Local VND or USD are both accepted. Banks are open Monday to Friday and some open on Saturday morning. In main cities, travelers' cheques can be exchanged at banks and some exchange bureau, but this can be very difficult in small towns. ATMs can  be found in major citiesHanoi and Ho Chi Minh city, Hoian, Haiphong so do not depend on any kind of bankcards ( e.g. credit cards...) as your main source of funds.

Vietnam Currency Exchange rate in Jan,2007

1000 VND = US$0.06
2000 VND = US$0.12
5000 VND = US$0.31
10.000 VND = US$0.62
20.000 VND = US$1.24
30.000 VND = US$1.86
50.000 VND = US$3.11
100.000 VND = US$6.22
150.000VND = US$9.34
200.000 VND = US$12.45
300.000 VND = US$18.68
400.000 VND = US$24.91
500.000 VND = US$31.14
1.000.000 VND = US$62.29

Source: http://finance.yahoo.com