Welcome to the JavaRanch Kathy.
If your employer is willing to pay for a new book then I would say that it is necessary. If you have to pay for the book yourself, then I would say that it is optional. A lot of people passed the 1.4 certification before any of the new study guides were available. I'm sure that you can also. Just ignore the chapters on AWT and IO.
The difference between 1.2 and 1.4 is as follows.
The 1.4 exam removes the AWT and IO topics but adds assertions and a couple new classes in the collections framework--
LinkedHashMap and
LinkedHashSet. The wrapper classes and the Object.hashCode and Object.equals methods are further emphasized in 1.4.
Everything that you need to know about assertions is available in the document
Programming with Assertions.
For more information, please see the
objectives for the 1.4 version of the exam.