On his Google Earth Blog, Frank Taylor has made available an online KMZ file that, when opened, will allow you to load a HUGE amount of data related to Hurricane Gustav into Google Earth (GE). The basic version of Google Earth is FREE, and may be downloaded from the GE website.
My advice is to selectively turn the various "layers" on and off. Turning all the layers on at once leaves the map virtually unreadable.
I'm sure other KML files and data layers will become available over the next several days as we all anxiously wait to see where Gustav tracks.