using position:fixed alone is just fine when you don't have a header or logo at the top of your page. This solution will take into account the how far the window has scrolled, and moves the div when you scrolled past your header. It will then lock it back into place when you get to the top again.
if($(window).scrollTop() > Height_of_Header){
//begin to scroll
$("#div").css("position","fixed");
$("#div").css("top",0);
}
else{
//lock it back into place
$("#div").css("position","relative");
}