I was able to install g4ptool by moving the tool into the tools folder in c:/processing sketch book/tools. After installing the tool I had errors. I then used Processing V1.5.1 , G4P Tool version 1.1.1, and V1.7.6 of the G4P library and got these errors:
Exception in thread "AWT-EventQueue-0" java.lang.NoSuchMethodError: processing.mode.java.preproc.PdePreprocessor.scrubComments(Ljava/lang/String;)Ljava/lang/String;
at g4p.tool.gui.GuiControl.getSketchSizeFromCode(Unknown Source)
at g4p.tool.gui.GuiDesigner.<init>(Unknown Source)
at g4p.tool.G4PTool.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:642)
at java.awt.EventQueue.access$000(EventQueue.java:85)
at java.awt.EventQueue$1.run(EventQueue.java:603)
at java.awt.EventQueue$1.run(EventQueue.java:601)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:612)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)