when i did mine i just went to immigration and gave them the two passports think i had to fill a form or get something copied but it was all done there and then. dont remember paying anything either
never been to Vientiaine. but visa on arrival at Savanaket is no problem. assume its the same at V.just fill in a form and give them your passport cash and photo.believe the visa is now 2000 baht was 1500