You can get a taxi right outside the arrival terminals. From the airport to Peking University is about 30 km. The fare should be less than 150 Yuan. If you take the Taxi, you may show the following tag to the taxi driver about how to get to the guest house.
Building 9, Zhongguan Xinyuan Global Village, Peking University,
126 Zhongguancun N St, Haidian, Beijing, China, 100871