You're already to convert your mp3s…but where are they?
You can go to the Window's Start button, followed by "Find", followed by "Files or Folders". Type '*.mp3' without the single quotes and make sure "My Computer" is selected in the "Look In" control. Then press the "Find Now…" button. This will take awhile and scan your hard drive for all your mp3s. Then you just have to right click on the ones you want to convert!