Как вариант...
<!DOCTYPE html>
<html>
<head>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<!--
<link rel="stylesheet" type="text/css" href="tmp.css" />
-->
<style type="text/css">
label {
display: block;
}
</style>
<script type="text/javascript">
$(document).ready(function (){
$('#options input:checkbox').change(function (){
setValue();
});
loadData();
});
function setValue(){
var dlm='';
var val='';
$('#options input:checkbox').each(function (){
if (!this.checked) return;
val=val+dlm+this.value;
dlm=';';
});
$('#txt').val(val);
};
function loadData(){
var a=$('#txt').val();
a=a.split(';');
for (i=0; i<a.length; i++) {
$('input[value="'+a[i]+'"]').attr('checked',true);
};
};
</script>
</head>
<body>
<div>
<textarea id='txt' rows = "5" cols = "120" name = "txt">one;two</textarea>
</div>
<div id='options'>
<label>
<input type="checkbox" value='one' onchange="test();"/>one
</label>
<label>
<input type="checkbox" value='two' onchange="test();"/>two
</label>
<label>
<input type="checkbox" value='three' onchange="test();"/>three
</label>
</div>
</body>
</html>