if you "right click" or press and hold, on the file, you should get an option to "set as ringtone" or in wm6, you can library browse though the audio files, hit the menu button with the file selected, and go to "set as ringtone". Also you can go to alerts in the settings, and set specific files which are in your ringtones folder to be synonymous with specific events, such as new email, or new phone call.