Without knowing which OS you're running, I'll assume it's an NT-based OS like W2K or XP. Open Windows Explorer | Tools | Folder Options | "File Types" tab | Scroll down to the file type / extension of which you'd like to change the icon (in your case the *.m4a file extension) | "Advanced" button | In the Edit File Type dialog box that opens, click the "Change Icon" button... and browse to the folder, *.dll, etc. that contains the *.mp3 file icon that you'd like to use.