Visa for China in Vientiane, Lao I am an American what are the reguirements

does anybody know if you can travel by bus from Lao into China, Yunna? Also what are the requirements to get a China Visa in Vientiane being a American citizen? I will be in Lao towrds the end of October, 2012. Do you need proof of a return ticket leaveing China before they will allow you to enter China?