There is a program that is like a visual aid but it does not work with gpp-win or gx dev. Its a stand alone program that uses mitsi ladder in one half of the screen and a visual virtual machine in the other.
To be honest, I thought it was poor and not for real programmers.
Its sort of for management that program one of the examples (like an auto garage door) then they can proclaim that programming is easy and they dont know what all the fuss is about.
I can't remember the name but it does exist.
There is also an add on to gpp-win called LLT (logic ladder test)
This simulates a real PLC without one being connected.
You can program timelines for different inputs on and off and it is a very good first test of your logic.