Javascript - Javascript doesn't work in ie

Hi,

I am new to javascript, i have this little bit of code i have put together to only display a text field deppending on yes/no in a previous form field now this works fine i uploaded it to the server and it works great.

The problem i have is i use firefox, when i looked at the page using ie 6 and 8, suddenly the form is not even visible and there is just a blank space. As a newbie i can not see why this doesn't work and so if anybody has any pointers it would be much appreciated.

Thanks

Stan

[code]
<!--
function displayoptional(){
var a= document.forms['capform'].elements['camper'].value
if(a =='camper'){
document.getElementById('optional').style.display = '';
}
else if(a =='owner')
{
document.getElementById('optional').style.display = 'none';
}//endif
}//end displayoptional function
[code]