In short, these are the steps:

  1. Check out PDI from SVN source (for example
  2. Fix all build errors
    1. IMHO most often, only the SWT.JAR has to be fixed.
      Check: Project -> Properties -> Java Build Path -> Libraries -> swt.jar
      You have to use the correct swt.jar, depending on your platform. So remove the incorrect one and add correct swt.jar manually. For example use 'lib-ext/win32/swt.jar' on Windows XP 32bit.
    2. Check that you have a JDK1.6 Java Runtime installed in your Eclipse workspace. Set it as default.
    3. Check that the Kettle project Java compiler setting is set to "1.6" (else you will and up having ca. 32000 errors)
    4. In case of error "SwingXulLoader cannot be resolved",
      configure Project -> Java build path -> Libraries -> Add Jar (at the end) "test/libext/pentaho-xul-wing-TRUNK-SNAPSHOT.jar"
  3. Create Debug Launch configuration
    1. Name: Spoon
    2. Main class: org.pentaho.di.ui.spoon.Spoon
    3. Arguments for VM: -Xmx950m -XX:MaxPermSize=256m

Now, you should be able to start Spoon with regular 'debug' launch mode.