$(function() {
// OPACITY OF BUTTON SET TO 50%
$(".sm_btn").css("opacity","0.5");

// ON MOUSE OVER
$(".sm_btn").hover(function () {

// SET OPACITY TO 100%
$(this).stop().animate({
opacity: 1.0
}, "slow");
},

// ON MOUSE OUT
function () {

// SET OPACITY BACK TO 50%
$(this).stop().animate({
opacity: 0.5
}, "slow");
});
});