What I really want is just an easy way to do various real-time plots and status indicators on my Windows PC screen to show data coming in on the serial port, and some control buttons to send commands back on the serial port
Look at how Processing was used to provide a UI for the PID libraryhttp://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1243714052
"Processing" is nice and user-friendly, but doesn't seem to be really designed for this.
It's based on Java, so I looked at just using the Java Swing GUI setup. But from a quick look, that's not easy to jump into with no experience in that area.
Java, but UIs developed in Processing do not use Swing to build the GUI.
Read the source code for the example above.
Because Processing is written using Java, it runs on OSX, Windows, and even Linux boxes.
Go to http://www.processing.org/
and follow the Download link to download Processing for your "Windows PC".