How can I Install Cocos3D for iPhone/iPad?
As stated on the official cocos3d site:
Once downloaded, unzip the file and follow the instructions in the README document to run the install-cocos3d script from an OSX Terminal session. Since cocos3d is built on top of cocos2d, you will also need to download the latest version of cocos2d before running the installation script.
here goes the solution very explained with screen shots
http://www.techipost.com/2011/02/20/installing-cocos3d-for-iphoneipad/
You can also download and install Kobold2D, which includes Cocos3D and a readymade Cocos3D example project that works out of the box.