Javascript Error, div layers appearing and disappearing

[Fareon]

I am currently working on this page...

http://www.quickmedical.com/cart/checkout.php?act=checkout

And if you click on the Different Shipping Address checkbox, then a div layer with a bunch of input boxes appear. However I am trying to get that to work with the CVV Number field as it is already in a div layer, I just can not get it to appear and dissapear like the other div layer. There is too much code for me to post here so please check out the page and hit view source to see the code.

[_Aerospace_Eng_]

try this
<script>

jhidden = 0;

function hide() {

if (jhidden % 2 == 0) {
document.getElementById('cvvfield').style.display= "block"
} else {
document.getElementById('cvvfield').style.display = "none"
}

jhidden++;
}

</script>