You get 5500 Kip from unlicensed moneychangers. They are everywhere on Thanon Phothisalat in Luang Prabang and on Talaat Sao and around the GPO in Vientiane. Spend the night there. Spend your last Kip in one of the noodlesoup shops, then head to the Lao Immigration and walk 500 meters to the Vietnamese border. Traffic on either side of the border is still very erratic, so start early in case you have to wait somewhere on the way.
Vietnamese visas are available at the embassy in Vientiane.
The National Library has some books in English and French. As a tourist you cannot check them out, but the staff will happily make photocopies and bind them for 100 Kip per page. There is a Royal Air Cambodge and Vietnam Airlines booking office at Lao Hotel Plaza. Vang Vieng - Immigration here is keen on you registering. Admission is 3000 Kip.