Face book provide 2 ways of add fb-like button on your website:xfbml and iframe version
If you want to show it on a popup window, you should use the iframe version
 
 

?<iframe src="http://www.facebook.com/plugins/like.php?href=YOUR_URL"
 scrolling="no" frameborder="0"
 style="border:none; width:450px; height:80px"></iframe>