Code dilema --> '".NULL."' or '.NULL.' or ...

Hi, I'm having troubles trying to insert form data into a mysql db, the thing is my client wants table data to be splitted, I mean some data comes from the first form, and the rest from another form. Then this is a portion of the php script. // Add together proper fields to enter birth date $fecha_nac = $ano_nac + "-" + $mes_nac + "-" + $dia_nac; // Open mysql db mysql_select_db("intertur"); // SQL query insert all data into a table $query = "insert into RegistroPersonas values ('".NULL."','".$nombre."', '".$apellido."', '".NULL."', '".$direccion."', '".$ciudad."', '".NULL."', '".NULL."', '".$pais."', '".$telefono."', '".$fax."', '".$email."', '".$login_usuario."', '".$clave."', '".$fecha_nac."', '".NULL."', '".NULL."' '".$sexo."', '".NULL."', '".NULL."', '".NULL."', '".NULL."' )"; ----> My problem is NOTHING gets inserted !!! ----> I filled all empty fields with NULL values ----> It connects to the db but does nothing else // Do query $result = mysql_query($query); // this script has a form at the end, where the remaining fields are // filled // and calls the next script, where the tables are altered // there and the empty fields filled with the values retrieved I suppose to use Update in the next script , to enter remaining data, but I'm not sure because the first field auto increments, and is the primary key. TIA Rick AXIS Computers