MrLao4ever, Yes, it takes around 10 hours from Vientiane to Pakse on a VIP bus. Maybe longer on a regular bus.
VIP buses are the comfortable buses with air conditioning and a toilet, and they only stop once for a 10 minute break in Savannakhet.
The regular buses stop frequently for toilet breaks and picking up/dropping off passengers along the road. However, the fare is cheaper.
Chuck, This bus station is situated in the Kua Din area of Vientiane.
The buses at the southern bus station go to Bolikhamxay. You have two options. You can catch a regular bus, or one of the pickup trucks similar to the pictures below. They are also located at the southern bus station.