In the first frame make a Dynamic text box, and set the var "time_left". Add this Action script to the frame:

stop();

setInterval(countdown, 1000);

time_left = 10;

function countdown() {

time_left = time_left-1;

if (time_left<=0) {

gotoAndStop(2);

}

}

Make a new frame and write something in it... Now it counts down from 10 to 0. If it doesn't work, look at the fla.