The extra CD of tools included in OS X to let you make programs and so on. Compilers, debuggers, and other little utilities. In later OS versions that install from a DVD, there is, of course, no “extra CD”.
No CD: see WhereToGetApplesCocoaCompiler from AppleDeveloperConnection
Once you have the DeveloperTools packages, be sure to perform the installation on the same partition where OS X is installed.
*XCode *InterfaceBuilder *ProjectBuilder *MallocDebug