We had booked the minivan, a night's accomodation in Chiang Khong and the boat altogether. The "guesthouse" looked ready to fall into the Mekong river. The doors were locked with a padlock and whilst there was an actual toilet we had to "flush" it ourselves by tipping water from the adjacent bucket. After an average sleep - we were woken in the early hours by music blaring out from across the river in Laos - we packed up, had breakfast and jumped into a mini-van to Thai Immigration.
After getting stamped out of the country we crossed the Mekong to Laos on a small "speedboat" - aka canoe with a motor - and joined queue for Laos Immigration. We already had our visas so easy enough. Ben changed some Thai Baht for Lao Kip and we jumped in a tuk-tuk which took us further down the river where we got on the Slow Boat.
The Slow Boat is a large barge style boat into which they put half a dozen comfy aeroplane style seats and 50 small wooden benches designed to cause several back pain that will last several days after your arrival in Luang Prabang even after a Lao back massage.
We bought cushions for 40 Baht each which I think made a diference but Ben reckons didn't help.
We got to the boat after several stops - the above sounds much easier and simpler than it was. We had to show our passports numerous times and wait for the group to reconvene. We were sat on the boat at about 10.30 I think and it eventually left just after noon. I was anxious to get on and get a seat because you hear stories how people end up sitting down the aisle and in with the bags at the back of the boat next to the engine.