There's an interesting thread over at Pandagon about Salma Hayek's breasfeeding her thirteen month old child: http://pandagon.net/index.php/site/comments/boobie_jokes/
How long is it appropriate to breastfeed? It's none of my frakking business, but it would not be outside the range of normal variation in higher primates to extend it for as much as four to five years. So, I'm not one to comment on Ms Hayek's preferences in this regard except to accept and affirm them as her choices to make. More power to her and her child.
Is it appropriate to admire the breasts of a lactating woman? It depends on how you express your admiration, I reckon, but it would be damn near impossible for me not to admire Ms Hayek's features. I have always admired her beauty and talent since I became aware of her. She is extremely attractive, and she is no less attractive now that she is lactating.