Writing hack for IE6 & IE7 in a single line. This was the easiest way to put it in three line. If you put underscore it will work on IE6 in any property ( like.. margin, height, backgound etc..) .If you put .dot it will work only on IE7. Just Follow the same structure as per the example.

selector {
height: 100px ; /* Firefox */
_height:120px; /* IE6 */
.height:130px; /* IE7 */
}