SetInterval?

I am trying to use the SetInterval COLOR=seagreen [/COLOR] I guess thats what u call it to Display an external Image for 60 seconds and then randomly select 1 of 4 external .swf files that are in the same directory and display it for 60 seconds and then pick another and continue on until each file has been selected and displayed and then when all of the .swf files have been displayed bring the image back up and start the whole process over again. I was reading a page I found on the net but it was WAY over my head and that is where I got the SetInterval Code I found. Here is a Sample of the code I have

Movienum = Math.floor(math.random()*5);
displayTime = 5;
countDown = displayTime--;
	if (displayTime == 0)
		clearInterval(timer);
		Movieum;
timer = setInterval(countDown, 1000);
if(Movienum == 0) loadMovie("1.swf", 0);
if(Movienum == 1) loadMovie("2.swf",0);
if(Movienum == 2) loadMovie("3.swf", 0);
if(Movienum == 3) loadMovie("4.swf", 0);
if(Movienum == 4) loadVariablesNum ("img1.png", 0);

Thank you in advance
Ryan