This is wonderful... you install Xcode using App Store in OSX 10.7 a.k.a. Lion. It will not install itself when done, instead it will create an 'installer' icon in the Applications folder. Good, click on it and wait a little while. The expectation is that g++ will be available in the terminal CLI after that, right? Not! After that, you need to select in Xcode menu "Open Developer Tool->More Developer Tools..." which leads you to a download site. Obviously, just having an apple ID is not enough, you need to register yourself as a 'developer', authenticate yourself with the code received by email and then be graced with a 172MB download that hopefully will have the basic tools that any *nix variant take as granted. Way to go, apple!