The easiest method is to simple code the feature that you want, as you can control more than just the size of the window. For example
<a href="#" mce_href="#" onClick="MyWindow=window.open('http://ilonsmartserver.com,'MyWindow','toolbar=no,location=no,directories=no,status=no, menubar=no,scrollbars=no,resizable=no,width=600,height=300'); return false;">Click Here</a>
In this case, the new window would not have any of the usual interface items (toolbar, scrollbars, etc) and would be 600 x 300 pixel.