Building on Chad's answer, you also want to add that function to the onload event to ensure it is resized when the page loads as well.
jQuery.event.add(window, "load", resizeFrame);
jQuery.event.add(window, "resize", resizeFrame);
function resizeFrame()
{
var h = $(window).height();
var w = $(window).width();
$("#elementToResize").css('height',(h < 768 || w < 1024) ? 500 : 400);
}