Some help with Javascript checkboxes

How do I make Javascript checkboxes than needs to be checked ?
I have a site and I need something at the new user registration ( I agree with TOS ) and the TOS checkbox needs to be checked ...
Hope you understand my request

/edit : I found something related at DynamicDrive : http://www.dynamicdrive.com/dynamicindex16/acceptterm.htm
It's not the same thing but it can do the job

 

That's pretty simple actualy. Here's one way to do it:

<script type='text/javascript'>
function enableConfirm(checked)
{
	if(document.forms[0].check.checked == true)
		document.forms[0].confirm.disabled = '';
	else
		document.forms[0].confirm.disabled = 'disabled';
}
</script>
<form method='post'>
<input type='checkbox' name='check' onclick='enableConfirm(this.checked)'>
<input type='submit' name='confirm' disabled>
</form>

Code (markup):

 

you can also use the document.getElementByID method

function checkConfirm(chkID)
{
var chkBox = document.getElementById(chkID);
return chkBox.checked
}

use it like this

if( !checkConfirm('theCheckBoxID') )
{
alert('your error goes here');
}