You can book the hotels from

http://www.elong.net/

http://english.ctrip.com/ or directly from the website of the hotels:

 (1) Unisplendour International Center (four star)
    Location: in the heart of Zhong Guan Cun, outside the East Gate of Tsinghua   
    University.    
   Reservation：（86-010）62791888
   Website: http://www.uniscenter.com/

(2) Wenjin Hotel (five star)
   Location: outside Tsinghua South Gate.
   Reservation：（86-010）62255566
   Website: http://www.hotelbtoc.com/hotel/beijing/wenjinhotel.htm   

(3) Beijing Jadepalace Hotel (four star)
   Location: No.76 Zhichun Road, Haidian District, Beijing. 2 Km to Tsinghua University.
   Reservation：（86-010）62628888
   Website: http://www.jadepalace.com.cn/

(4) Beijing Xijiao Hotel (four star)
    Location: No.18 Wangzhuang Road, Haidian District, Beijing. 1 Km to Tsinghua    
    University.
    Reservation：（86-010）62322288-5606/9108
  Website: http://www.xijiao-hotel.com.cn/index.htm