In the community translations page, there is 3 chinese language packs : Chinese (Hong Kong SAR), Chinese Simplified (China) and Chinese Traditional (Taiwan)
Direct link : http://www.magentocommerce.com/langs
To install a language pack you have just to copy the chineses folders in the language folders of your Magento directory, and setup in the admin panel to be the default language.
If those versions of Chinese are not good, you can translate yourself all the sentences by editing the default csv files (right column) located in the “en_US” folders.
I hope this will help you…