Class paths from Project | Properties | Paths | Classes
  Class paths from Project | Properites | Paths | Required Libraries | Classes
     (And each library may itself have a nested required library list...)
  Class paths from the Tools | Configure JDKs | (selected jdk) | Classes

If your new package is in your project's source tree, it will be included automatically.

If your new package is a 3rd party library (ie classes or jars for which you have no source files) then stick them somewhere outside your project and define a library for them. Then add this library to your project's required libraries list.
2001-May-24 10:47am gyles19@visi.com