In reply to Vikki Haydock:
If your into culture stuff then the water puppets in Hanoi are well worth a visit. We found the beaches in Na Trang really good to and there is a nice one a bike ride away in Hoi An. Halong Bay was a real highlight of the trip, we stayed on a boat and went kayaking which was really enjoyable.
Travelling by train is a good way to meet local people, the rolling stock is pretty rickety and flying can cheaper and definetly quicker. We struggled to get train tickets (you have to pre book you can't just get on) at a sensible price via the net though this was a couple of years ago.
However had booked a fairly posh hotel for our first night after the flight. We e-mailed them and they arranged them all for about 20% of the costs we were being quoted online so the night paid for itself.
Hope you enjoy your trip it seems to be a bit of a love/hate thing, don't let any initial bad experience put you off at the start (we didn't have any the whole trip).