Gentlemen, I don't know what I did differently (besides reverting to the non-Putty key, which I swear did not work before) and...
Now it works.
At the moment I have no need for advanced features like remote file access, sound, or printing - just the ability to run a simple Java-based GUI running on the server. And that's looking great.
So - thanks so much. The support has been excellent.
Now I need to document this internally before I forget it all.
Best,