In the Windows Administrator Client, right-click on the server name, and choose 'System Parameters'. From there, you can choose System-wide settings for logging. Enable or disable the messages you'd like to appear in the System Log.
For fine-grain control over Application Group specific messages, go into the Application Group of your choice, right-click and choose 'Update', then go to the 'Message Logging' tab, and select which messages you'd like to appear in the System Log.
-JD.