NateOn is a very popular messenger system in Korea. The native client is only available for Windows, but someone developed a plugin for Adium (Mac OSX client for multiple chat systems). The latest version of Adium is 1.5.1 (as of July 15, 2012), but I have to use 1.4.5 in order to use with SIPE MS Messenger plugin which is compatible with my work messenger system.
Resources:
Install Adium first, and download the NateOn Plugin, unzip it, just double click on the plugin file. The plugin files are installed at: /Users/[YOUR USER NAME]/Library/Application Support/Adium 2.0