Transparency is somthing which will work differently in all browsers. For working with the transparency we have to create a four statements. See the example its set to 50%.

.selector {
filter:alpha(opacity=50); /* IE6 */
-moz-opacity:0.5; /* FF2, FF3 */
-khtml-opacity: 0.5; /* Safari */
opacity: 0.5; /* FF2, FF3, Safari */
}