Visas and border crossings forum

From the Visa and border crossings FAQ:

"Na Maew / Nam Xoi
Open 08:00-17:00
This crossing opened in 2004 and for those coming from Vietnam it offers convenient access into the boondocks of Laos' Hua Phan province. It is a short ride from the border to Sam Neau.

Chunk79 reports from 13 October 2006: Six of us went through no problems although the Vietnamese check every bag quite thoroughly so it takes some time. To get there, we caught a bus from Sam Neua at 06:20 (although it didn't leave until 07:30) which ran all the way to Thanh Hoa in Vietnam (100,000 kip) arriving there about 16:30. There are lots of local buses north to Hanoi (3 hrs 40,000 dong) from Thanh Hoa. In theory there should be a more direct way to Hanoi but it wasn't evident from the bus. Not sure if the bus runs every day - it is definitely the only bus that goes all the way through.

There are songtheaws to the border from Sam Neua for 21,000 kip but there isn't much on the Vietnamese side to pick you up.

The bus doesn't go into Vieng Xai so if you choose to stay there (not a bad option in my opinion - it makes more sense than doing a day trip if you are heading over the border) you would need to wait for it on the main road outside of town."

You're looking at a very full day of travel to get from Luang Prabang to Sam Neua, where you'd overnight and then press on as per the instructions above -- so you're looking at at least two full days of travel.