<select style="width: 155px; height: 20px;" onchange="this.value && frUrls(this.value)">
<option>Клац</option>
<option value="http://1.ru,
http://2.ru,
http://3.ru,
http://4.ru, http://5.ru" > Links </option>
<option value="http://6.ru,
http://7.ru,
http://8.ru,
http://9.ru, http://10.ru" >Links2</option>
</select>
<br>
<script type="text/javascript">
var frInt = false, time = 1000;
function frUrls(b)
{
if(frInt) clearInterval(frInt);
var a = 0, b = b.split(','), c = document.getElementById('main');
c.src = b[0];
frInt = setInterval(function()
{
a++;
c.src = b[a];
if(a+1 == b.length) clearInterval(frInt);
}, time);
}