if you use the free version i think there is a way to save out in google earth(.kzm) then rename to zip, extract and convert the resulting .dae (collada) format via fbxconverter to something useful like .obj or .3ds which then could be handled by most .x export-capable apps. I only did some research on the matter and if you are lucky to own the pro-version that exports .3ds natively. So you may be better off with milkshape or another lowcost suite for modeling....
@ Aaagreen these are the tools of sketchyPhysics, a physics simulation engine for sketchup. Google or Youtube it, it's loads of fun!
I am Jacks complete lack of surprise.