Over the last few years there have been quite a few tools developed, including from Esri, that generate .kml files from your Shapefiles. They can be tough to use at times or easy but none are as satisfying as running from OGR GDAL at the command line. Why? Who cares, its just cool to be able to run things from the command line. Go here to follow Google's how-to:http://code.google.com/apis/kml/articles/vector.html
If you download and install GDAL OGRhttp://trac.osgeo.org/gdal/wiki/DownloadingGdalBinaries
Go here at Google Code http://code.google.com/apis/kml/articles/vector.html and follow the easy steps. And then open up your new .kml in Google Earth.
Even later on you can customize more with libkml. http://code.google.com/p/libkml/
