When you install Ringleader you must first setup your ringtone associations so that Ringleader knows what applications map to what ringtones. To do this, you must go into each of your application settings and re-choose your notification / ringtone sound using Ringleader. For example, to enable Ringleader to manage your Gmail ringtone, you would open the Gmail application and then select "Settings" from the menu. From within the settings menu for Gmail, choose "Select ringtone". You will be presented with a dialog entitled "Complete action using" and you must choose "Ringleader" at this point. You will now be able to select your desired ringtone and once this ringtone is chosen, you should now be able to see Gmail in the "Active Ringtones" tab within Ringleader. This is a one-time process to setup each of the applications that you want to manage within Ringleader.
You may have to reset your system defaults if you are not given an option to choose Ringleader as your ringtone picker. To do this, go to your Android Settings --> Applications --> Manage Applications and search for "Android System". Tap on "Android System" and then choose "Clear defaults". If you are using another application as your default ringtone picker, then you would need to clear that application's defaults instead.