to create a popup window you need javascript
(javascript:window.open('myPopup.aspx",other properties here)
this site will make the js you need for a popup window : http://javascript.internet.com/generators/popup-window.html
you should not need to call it from codebehind you just call it from client side javascript.
this is what i use all the time :
function genericPopup(href, width, height, scrollbars){
var param = "width="+width+", height="+height+", scrollbars="+scrollbars+", resizable, status";return window.open(href, "", param);
}
then i just pass it the href (url), width, height, and if we want scroll bars or not.
to call it from a link you would use
<a href="MyDestinationPage.aspx" onClick="genericPopup(this.href,300,300,no)">Click for popup</a>
if you NEED to call it from serverside you need to inject the javascript into codebehind and use RegisterClientScriptBlock method (which is complicated) if you can avoid doing it from code-behind i would.
mcm