Ogle Earth wrote great KML to track Space Shuttle Discovery and ISS on Google Earth, by a Network Link to scrape cordinates from NASA website.
It shows actual altitude of the orbiters in good shape.
KML is available in this blog entry.
This KMZ is updated every 1 minute, and CelesTrack/Altemis based one (white circle placemark titled STS 114 and ISS ZARYA) is updated every 8 second. So it’s a little bit behind but no problem.