Well i have a transparent div or the background is set to transparent :) css:
#lowerLayer
{
    position: fixed;
    top: 0px;
    left: 0px;
    right: 0px;
    bottom: 0px;
    width: 100%;
    height: 100%;
    background-color: Transparent;
    cursor: help;
    z-index: 1;
}
The div is placed right under the tag.. and under there i have a blueprint layout.
jquery(this is run in $(document).ready):
$("#lowerLayer").click(function() {
    $(this).fadeTo("fast", 0, function() {
        $(this).hide(0);
    });
});
My layout works perfect in Opera 10 and i guess it works in Opera 9 to... but IE 7 bugs layers that have lower z-index are acting as they are above the transparent div...