Trying to create a countdown timer

Hi. I only have Flash 5… and I tried to use the tutorial to create a countdown timer… but it uses Flash MX. For some reason the code is not working and I can’t figure out why. I believe the problem lies in this function: counter.onEnterFrame = function(){

The tutorial can be found here:
http://www.kirupa.com/developer/mx/countdown.htm

I couldn’t find a good countdown tutorial on Flash5… so I tried to use this one… so far to no avail. I could really use some help. Thank you.