Most expats filing their own taxes seek the help of an accountant with facility in the tax laws of their home country as well as those of Vietnam. Many companies will include tax/accounting services as part of their expat compensation packages, or can refer employees to reliable tax advisors.
Price Waterhouse Coopers provides international tax advice for expat residents in Hanoi:
#701, 7th Floor, Pacific Place
83B Ly Thuong Kiet Street
Tel:  (4) 3946 2246
David Wisdom provides reliable advice for American expats working in Vietnam:
13226 Frame Ct.
Poway, CA 92064-3658
U.S. Fax number: +1 858-748-3812
The best online guide to Vietnam’s tax laws is on the Price Waterhouse Coopers website here with a 2012 update on taxes and legal services: