$.fn.opacity = function(amount)
{
    if (amount > 1) amount = 1;
    if (amount < 0) amount = 0;
    
    if ($.browser.msie)
    {
        amount = (parseFloat(amount) * 100);
        this.css('filter', 'alpha(opacity='+amount+')');
    }
    else
    {
        this.css('opacity', amount);
        this.css('-moz-opacity', amount);
    }
    
    return this;
}