как минимум вот так
<html>
<head>
<style>.btn1 {
margin: 2px;
padding: 2px;
width: 32px;
height: 32px;
float: left;
cursor: pointer;
border: 1px solid gray;
background-color: #ccc;
color: white;
padding: 3px;
}
.btn1:hover { }
.btn2 {
margin: 2px;
padding: 2px;
width: 32px;
height: 32px;
float: left;
cursor: pointer;
border: 1px solid gray;
background-color: #cco;
color: white;
padding: 3px;
}
.btn2:hover { }
</style>
</head>
<body>
<div align="center" style="width:640px;background-color:#ddd; margin:auto;margin-top:5%; border: solid 1px black;
height: 340px;
}">
<div style="float:left;"><embed *!*id='flash'*/!* src="http://javascript.ru/forum/image.php?u=17434&dateline=1322593884" width="320" height="340"></embed></div>
<div><button class="btn1" onclick='document.getElementById("flash").src = "http://javascript.ru/forum/image.php?u=42910&dateline=1436249386"'>1</button></div>
<div><button class="btn2" onclick='document.getElementById("flash").src = "http://javascript.ru/forum/image.php?u=2844&dateline=1327668727"'>2</button></div>
</div>
</body>
</html>