Keep in mind that you publish KML through Map Services, not 3D Globe
Services, even if you are publishing 3D data such as extruded
buildings.
So you'll end up copying the 3D layers from ArcGlobe over to an MXD
Map document to pubish the KML capability.
The doc also describes this,
http://webhelp.esri.com/arcgisserver/9.2/dotNet/manager/publishing/kml_s
ervice.htm, but note that you can publish out the data as an image, or
overlay (basically a map export to image for a given extent) or you
can pull the vector features over as KML (this helps to support popups
for the data in Google Earth). The parameter setting to the URL that
you use for the KML\Map Service to control this is "composite=true" or
"composite=false".
Does this help?
Sam