THE PILOT STATED THAT DURING LEVEL FLIGHT AT 9000 FT, HE NOTICED SMOKE COMING FROM UNDER THE INSTRUMENT PANEL, FOLLOWED BY A VIBRATION FOR 15 TO 20 SECONDS. HE DIVERTED AND LANDED AT LOUISVILLE, KY WITHOUT FURTHER INCIDENT. AN EXAMINATION REVEALED THAT THE RUDDER TRIM TAB ACTUATOR ARM HAD SEPARATED FROM THE TAB. ALSO, THE TAB AND MOST OF THE RUDDER HAD SEPARATED FROM THE VERTICLE STABILIZER. MAINTENANCE HAD BEEN PERFORMED IN THE AREA OF THE RUDDER TRIM TAB ACTUATOR ARM ATTACH AREA. FOUR POPPED RIVETS HAD BEEN USED TO ATTACH A SKIN PATCH (UNDER THE RUDDER TRIM TAB BRACKET). EIGHT RIVETS WERE USED TO ATTACH THE BRACKET TO THE TRIM TAB. NONE OF THE 12 RIVETS MET THE STANDARD OF DEFORMING/EXPANDING THE RIVET TO 1 AND 1/2 TIMES THE ORIGINAL DIAMETER. AN EXAMINATION OF THE LOGBOOKS FAILED TO REVEAL WHEN THE MAINTENANCE WAS PERFORMED.