Those are conditional comments.
The <!--[if IE..
comments are generally used for including some custom code in the HTML file only if the browser is some version of IE.
Specifically the code you posted detects multiple versions of IE including a Windows Phone 7 browser and defines CSS classes on the html root element accordingly.
This allows you to write CSS targetd specifically for that browser like this:
.iem7 .my .selector {
/* this rule will apply only if the browser is ie on windows phone 7 */
}