<html>
<head>
<title></title>
<script type="text/javascript">
function showText(){
var pole = document.getElementById('checkbox');
if(pole.checked==true){
document.getElementById('text').style.display='block';
} else {
document.getElementById('text').style.display='none';
}
}
</script>
<style type="text/css">
#text {
display:none;
}
</style>
</head>
<body>
<input type="checkbox" name="checkbox" id="checkbox" onclick="showText();" /><br />
<input type="text" name="text" id="text" />
</body>
</html>