Is it possible to display the UCI commands being sent between a chess engine and Winboard/xboard?
An UCI chess engine doesn't run directly in Winboard/XBoard. You have to use an 'interpreter' progream like Polyglot. If you want to know how a chess GUI communicates with an UCI engines use Arena and press F4. If you want to use another GUI you may take a look to UCIPlug.exe.
Google 'polyglot' or 'uciplug' to find out more..