The first step is to install Xcode. That will give you all of the g++ commands in the Terminal. You already have vim, etc. so once Xcode is installed the Mac's Terminal will operate the same as any Linux machine. If he is just now learning C++, I would advise sticking with the Terminal for now. As some point he may want to build true MacOS X applications with Xcode, but that wouldn't help with a class.
Thank you all. Unfortunately, he left the installation DVD's home. Guess I'll have to mail them to him.
If he is at a university he should be able to sign up for a free developer account and download Xcode fairly quickly.
Can any of you tell him how he can save a file as a .cpp, though? Thanks!!
That depends on what he is using. To write source code, one must use a plain text editor. Xcode includes such an editor. There are a number of editors built in to the Terminal, such as vi and nano. Basic understanding of how to use vi would be very, very useful. If he wants something fancier, there is always TextWrangler and at least two dozen like it.