We did this exact trip last fall, flying on AA to NRT from JFK, then connecting on a AA code share operated by JAL using Air Vietnam metal. We went into Saigon, then then flew on Air Vietnam to Siam Reap, returning to Hanoi on Air Vietnam. We then picked up the AA code share-JAL operated flight on Air Vietnam metal back to NRT. I looked for these AA-JAL codeshares on Air Vietnam flights this year, and couldn't find them. Recently I remember that I read that AA was going to develop a partnership with Air Vietnam, and they were to have some code shares.

I remember that our AA JFK-NRT flight was late, and we thought we might be hung up at NRT for a day, but AA met a number of us upon arrival and walked us to the JAL departure lounge so that we could easily connect. My wife still talks about how cool it was making this connection.

There are a number of good hotels at Siam Reap, and we chose a property based on its close location to Angor Wat. When we arrived we found that the town was so small that it didn't matter much which hotel to choose as all are very close to the site. We were happy with the Sofitiel, but there is a new Meridien that was next door that now has the closest location to the site. The Raffles has a well rated property, and the Aman has a small property (about 15 roooms) that is soooo expensive. We spent 4 days, and we did not see all that we had hoped, but were busy every AM and PM. To aid tourists, many of the hotels have another business that provides guides, cars, and drivers to the site. We ended up with 3 nights at the Saigon Sheraton (the best hotel in the country), 2 nights at the Hanoi Sheraton with a night between these latter two at Halong Bay where we rented a car, guide, and driver at the Hanoi Sheraton.

If you have any questions about what to do, PM me. (Wish we could go again).