Thanks for the tip.
After a long pause I am having another go at it.
I added wxFormBuilder as a tool as suggested, and created a new dialog-based project.
Running the new project brings up the dialog with 'Welcome to wxWidgets'.
Double-clicking on WxWizDialog.fbp in the Others folder within Code::Blocks starts up wxFormBuilder.
As a timid test, I re-wrote the message text to 'Hiho' in wxFormBuilder, then saved.
Returned to C::B, rebuilt, and ran the program -- and it STILL displays the original message.
What am I doing wrong?