floater.js

    floatADivOnDomLoad : function(id, parentid) {
        util.doOnDomLoad( function() {
            if ($(id)) document.observe('scroll', util.floatADivOnScrollHandler.bind(this,id,parentid));
            // this is for the IEs                                                                                   
            if (window.attachEvent && $(id)) window.attachEvent("onscroll", util.floatADivOnScrollHandler.bind(this,id, parentid)); 
        });
    },
    
    // 
    floatADivOnScrollHandler : function(id, parentid) {
        var b = $(id);
        var b_height = b.getHeight();
        var par = $(parentid);
        var coff = par.cumulativeOffset()[1];
        var csoff = par.cumulativeScrollOffset()[1];
        var bottom_y = $('page').cumulativeOffset()[1] + $('page').getHeight() - $('page').cumulativeScrollOffset()[1];
        if (coff < csoff && b_height < bottom_y)
            b.setStyle({
                position: 'fixed',
                marginTop: '0px'
            });
        else if (coff < csoff)
            b.setStyle({
                position: 'fixed',
                marginTop: (bottom_y - b_height) + 'px'
            })
        else
            b.setStyle({
                position: 'static',
                marginTop: '0px'
            });
    },