Everyone using a Mac should make sure they have installed Xcode. It is included on the install DVD that came with your Mac.
For some of you, that may be all that you need to do. If you are still having problems, continue reading...
One of your classmates updated his version of SQLite using MacPorts. There are disk images and installation instructions online at this address:
http://www.macports.org/install.php
Download the appropriate disk image for your version of Mac OS X (they have Tiger, Leopard, and Snow Leopard). Mount the dmg, then double-click the pkg to install it.
Once the installation finishes, you can open a Terminal and type this command to install SQLite:
sudo port install sqlite3
If you have any trouble, MacPorts also has a User Guide at this address:
If git was not available for your version of Mac OS X, you can install it using MacPorts:
sudo port install git-core
MacPorts also includes Ruby 1.8.7 and RubyGems 1.3.7:
sudo port install ruby
sudo port install rb-rubygems