Do I need an Agent to process and get a visa to China?

Does one need to go thru an agent to get the Chinese visa. Information was that even when one get invitation letter by oneself this will not be accepted by you, because you have specific one you recognised.
I intended to witness the carton festival sometimes April, 2011, even when I have gotten contact with one of the organising agency in China, I was frustrated by the information received here in Nigeria that you may not accept the invitation
Your business environment and tourism has been a great asset of your country which one will like to exploit.
Please Kindly give your advise, I like processing my visa myself to ensure information and documents supply are genuine and authentic to my ability.
I work with the Nigeria government agency


Thanks