You may not drive in Vietnam without an Official Vietnamese Driving License.
An International Licence is only a Permit and still does not Qualify you to drive.
If you become a Resident of Vietnam with a Resident VISA ,,, then you can apply for a Drivers License. 

Hanoi

Transportation and Public Works Department
Address: 16 Cao Ba Quat, Dist. Ba Dinh
Tel . (04) 845.37.40

Ho Chi Minh

Transportation and Public Works Department

Address: 252 Ly Chinh Thang, Dist. 3
Tel: ( 08) 935.05.51 or 935.05.17