I recommend you go the reverse route - the hills are longer down than up!
Take the train to Lao Cai/Sa Pa and then grab a 'local' bus southbound. I suggest you get some good maps (Banda - Ha Noi - has a good book).
Buses run from town to to town where they turn around and return to their starting point. The roads are in rough shape and the buses have to travel slowly so schedules are unreliable.
Only take money under VND50,000 in denomination as there is difficulty getting change. There are ATM's in DBP and Son La and maybe even Lai Chau, now, where they are building huge damns.
Try to stay with the local minorities as they are such a joy to stay with - and leave a couple of extra bucks in the bedding they give you (saves face) rather than giving it to them.
The long arm of the law is there, naturally, and doesn't always wear a uniform. In every village there is a person (who everyone knows) who will require to inspect your visa and passport.
There is a strip of land all around the border which is prohibited to you but likely you will not get there unless you leave the road.
And don't forget to take plenty of memory, or film, as the views are stunning.
#2 CatBa has been a member since 5/3/2007. Posts: 349