Left click on the Server Name at the top, then right click and then click "Edit".
Open the ACL Window
On the tabs at the top of this Edit window click the "ACL" tab to access the ACL permissions.
If you click on the italicized "@all" you will see the default permissions for that channel.
Lets say you want to turn off the ability to "Whisper" other users. If you look at the first "@all" group at the top, they are able to whisiper. However since you are unable to change the permissions there you will have to change it in the lower "@all" group. You will check the "Deny" option and they will no longer be able to whsiper.
I have been overwhelmed with the level of professionalism and expertise displayed by Lightspeed and its affiliates! You guys rock! -Brian