In Civil 3D you can import a google earth image easily. File> import> Google earth image (or you can import image and surface). down side to this it does not come in on Grid. If you have for example a Mrsid image which comes with the associated files you can go to map>images>import image and if the right files are with it. It will bring it in on grid and at proper scale of your drawing.  I do not know what version of CAD your running if your running Civil 3D 2008/2009 there is a add on you must download to make sure this feature runs correctly.  You can do an internet search to find the add on you need. I hope this helps.

I want to put a map service(like google map) in cad as background. When I'm drawing, I can exactly know where should I put the shape. I want combine cad and gis. Use cad drawing vector picture and show it in my gis map.