On a product_info page that code will produce this in the html:
Or whatever the details are. It will produce that wherever you put it as long as it is not already in <?php ?> tags in which case you'd need to remove the ones in my code.
http://domain.com/index.php?main_page=product_info&cPath= 65 &products_id=181
So you could just put that code somewhere at the top of the page and you will see what it is outputing.
What you actually want to do is this:
But looking at it again I am not sure that the whole plan is going to work in that I am not sure the system will deal with the dynamic URL anyway. What that means is that I am not sure how the system will deal with the bit after the question mark. It might or it might not.
<iframe src="http://www.facebook.com/widgets/like.php?href=<?php echo zen_href_link(zen_get_info_page((int)$_GET['products_id']),'cPath= '.(int)$_GET['cPath'].' &products_id=' . (int)$_GET['products_id']); ?>"
style="border:none; width:450px; height:80px"></iframe>