I have an image on my site that I want to reload every 60 seconds without reloading the whole page (its a jpg if that matters)

This is what I have for a counter:

Code:
 var milisec=0 
 var seconds=10

function countdown(){ 
 if (milisec<=0){ 
    milisec=9 
    seconds-=1 
 } 
 if (seconds<=-1){ 
    milisec=0 
    seconds = 5
    document.getElementById("timed_img").innerHTML="loading...";
     //I'm thinking it needs to go here??
 } 
 else 
    milisec-=1 
    document.getElementById("clock").value=seconds+"."+milisec 
    setTimeout("countdown()",100) 
} 
countdown()
Above the image there's a simple input field for displaying the countdown
that time_img element is just a div surrounding the img tag I want to change

I'm just starting javascript programming (if that wasn't obvious)