XSLT 2.0 will process dates in international format (yyyy-mm-dd) using the expression ($x castable as xs:date) but you will first have to convert from the local format used in the USA, which you could do using substring operations.
In 1.0, take a look at the date-handling functions defined in
www.exslt.org.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference