Mach 84, there is a China Northwest Airlines' official web site and the web address is
http://www.cnwa.com, but their English version is currently under reconstruction, so you will not be able to visit it unless you can understand Chinese.
Additionally, China Northwest Airlines has a ticketing office located in Beijing Xidan Civil Aviation Ticket-selling Building, Xicheng District. In fact, the building is really just opposite Beijing Times Square. On CNWA's official web site (Chinese version), I found a phone number of its ticketing office I've just mentioned above, the number is 66017755, if you dial it from somewhere else in China, you have to add 010 (Beijing's city code) in front of the phone number and if you are calling from overseas, you need to dial 86 (China's country code) - 10 (Beijing's city code, but you don't have to put 0 in front of 10 if you call from overseas) - 66017755.
Anyway, I wish it helps a little bit and have a nice trip.