Hi,
1. Go to the Spatial tab in the properties page of your mesh.
2. Push the Assign... button
3. Set the projection parameters. It looks to me like your mesh is in UTM coordinate space so you'll have to:
a. set the projection to UTM.
b. set the zone
c. set the elipsoid
4. Push OK.
5. Now that you're back on the Spatial tab, select LatLong on the Projection listbox and press Apply.
6. Then "File->Save Copy As.." and select KML as the type
Hope this helps... Martin