****o Bich Thuy,
I had a physician from Spain e-mail me yesterday with the same desire that you are expressing. I don't know the correct procedure you will need to follow but I suggest that you decide what school you would like to attend here in the US and write to their admissions office about your desire. They are accustomed to advising foreign students about their admissions criteria as well as student visa requirements etc, so I believe that would be a good starting point at any rate.
Best of luck to you in your plans. If you get the opportunity to do this would you plan to return to Vietnam after graduating or do you hope to stay on in the Us and work as a nurse?