olahanz,
<html>
<head>
<meta charset="utf-8">
<title>…</title>
<style type="text/css">
#cont{width:70px;margin:5% auto;position:relative;height:70px;border:1px solid #000;}
#red,#green,#blue,#yellow{height: 40px;width: 40px;left: 10px;position: absolute;}
#red{background-color:red;left: 0;top:0}
#green{background-color:green;left:10px;top:10px}
#blue{background-color:blue;left: 20px;top:20px}
#yellow{background-color:yellow;left: 30px;top:30px}
#sel {position:absolute;left:0px;top:67px}</style>
<script type="text/javascript" src="http://yandex.st/jquery/1.4.4/jquery.min.js"></script>
<script type="text/javascript">
function showTR () {
$("#Show-Hid div[id]").show();
$("#Show-Hid #"+$('#sel1 option:selected').text()).hide()
}
</script>
</head>
<body>
<div id="cont">
<div id="Show-Hid">
<div id="red"></div>
<div id="green"></div>
<div id="blue"></div>
<div id="yellow"></div>
</div>
<div id="sel">
<select name="menu" id="sel1" onchange="showTR();">
<option selected="selected" value = "0">Choose a color</option>
<option value = "1">Red</option>
<option value = "2">Green</option>
<option value = "3">Blue</option>
<option value = "4">Yellow</option>
</select>
</div>
</div>
</body>
</html>