Thanks for all the info. I called Vietnam in San Francisco and they put me in touch with a travel agent here in Los Angeles. They were pretty useless tho, as they couldn't book me the flights to Siem Reap. I have come to the conclusion that it is easier to wait till arrival in SGN to buy the tickets (and cheaper too) but I am travelling with the wife and we have a tight schedule. Hence my trepidation to show up over there empty handed.