HPS just released the Direct Download version of Mexican-American War which you can find here:
http://www.hpssims.com/shopping/shopdisplayproducts.asp?id=4&subcat=5&cat=Early+American+Battles (http://www.hpssims.com/shopping/shopdisplayproducts.asp?id=4&subcat=5&cat=Early+American+Battles)