<script>
function openWnd(height, width) {
win = window.open(document.all['url'].value ,"Wnd", "HEIGHT="+height+",WIDTH="+width);
}
</SCRIPT>
<input name="url" value="">
<a onclick="openWnd(640,480)">640x480</a>
<a onclick="openWnd(800,600)">800x600</a>
<a onclick="openWnd(1024,768)">1024x768</a>