So I just saw this and decided to give you my two cents.
First of all the Vietnam Dong or USD/VND is 1 USD = 0.0000434461 vnd
So here the truth, if you were to look at a chart of the two currencies you see a lot of volatility which is what you need to trade. The problem is that there is not a lot of action as the VND is not the major currency. this means that the spreads would be wide and the pair may not be all that liquid.
For my money, it is best to stick with the major currency pairs where the spreads are razor-thin and there are always buyers and sellers.