Es simplemente CSS:
Código HTML:
Ver original<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- CSS -->
#contenedor {
height: 2000px;
width: 950px;
background-color:#39F;
}
#barra{
height: 20px;
width: 950px;
background-color:#999;
position:fixed;
bottom:0px;
margin:0 auto;
}
<div id="barra">Barra fija
</div>