Bukkit

// to get plugin:
if (this.getServer().getPluginManager().isPluginEnabled("MinecraftIM")) {
    MinecraftIM messenger = (MinecraftIM) this.getServer().getPluginManager().getPlugin("MinecraftIM");
}

// to send messages to the main user:
messenger.sendNotify("message"); // will automatically format color formatting :)

// to intercept chat messages (will need the plugin as a libary in your manifest):
(your class)  implements ChatMessageHandler {
    /**
    * Called when MinecraftIM receives a message from the authorized user
    * @param message what was received
    * @return if this method used the command, and don't do anything else
    */
    public boolean messageHandled(String message);
    /**
    * Called after any message received
    * @param fromUser what username this message came from
    * @param message what was received
    * @return if this method used the command, and don't do anything else
    */
    public boolean messageHandled(String fromUser, String message);
}
// then:
messenger.registerMessageHandler(your class);