I'm a wine professional, living in Bangkok and travelling frequently throughout South East Asia. I'm a huge fan of Laos and Cambodia and off the beaten track travel. Feel free to contact me at: www.facebook.com/mil.elephants
It's going to take a while to get to Nam Et, but boy is it worth it. The national park sits just below the Vietnamese border in Huaphan province, but it's more likely that you'll reach the park via Luang Prabang. The closest sizeable town to the park is Vieng Thong, also knows as Muang Hiam. There are several decent guesthouses but there are only few places to eat, especially at night. There's also a good local market where you'll find fresh and cooked food, medicine, clothing and hardware.
You're not going to find any burger joints here, and you're not going to find any 5 star resorts. What you will find is one of the most unique wildlife experiences in Asia and at the top of my must do list. The park is not easily and freely accessed and you must go with guides from the park via three different types of tours. But don't worry, you won't be sitting on a bus. The park is accessed by boat or foot depending on which tour you choose.
The original tour involved only one night in the park, a boat trip and night safari, the recently added yours involve longer trips and different forms of accomodation including the Nests, a form of tree hour that allows visitors to disappear into the tree canopy and watch the wildlife from a distance.
Trail camera's have caught up to 23 different Tigers, Gaur (an ancient form of cattle), Gibbons, Otters, Bears, Elephants and many small carnivores.
Your chances of seeing a Tiger are probably quite low, but if you don't go they are zero!
Here you'll find detailed information on getting to the park, timings and details of the tours and how to reach the park from Luang Prabang, Nong Khiaw, Phonesavan or Sam Neua. There are buses traveling through Muang Hiam from Vientiane, but I would not recommend such a long trip.