Google Earth imports are not supported in C3D2013. Search back in the group to see many other posts regarding this.
You could however try this
It doesn't matter, sir: the OP's looking for a way to import 3D terrain (vector) not imagery (raster).
As far as I know, the quickest way is to load a Dem file (e.g. a free Aster or SRTM) then create a surface based on it.
If you were to consider third party software, take a look at MapWorks Base, it will import GE surfaces and restore many other GE related functions, such as KML export, Image Import and more.
As others have stated, this is no longer an option within C3D 2013. My personal thoughts on this (and I honestly haven't heard from anyone official) is that Google got tired of C3D users using their data without paying for it and decided the best way around that was to force Autodesk to remove that functionality.
If you are in the United States, HERE is an alternative method to using Google Earth (and honestly, even if I had Google Earth, I would probably still go this route).
It's not as quick as the Google Earth option but it's (in my opinion) better, and it's free, publicly available, do what you want with it, you payed for it as a tax payer, data.
HERE is an alternative method
Already advised, Brian, exactly 3 posts ago (08-12-2012 05:55 PM), but... repetita iuvant, isn't it?