It suddenly occured to me to take another look at the warning log, and I found these messages:
9>..\..\Demos3\AllBullet2Demos\GwenTextureWindow.cpp(8): warning C4099: 'MyGraphWindow' : type name first seen using 'struct' now seen using 'class'
9>          c:\users\etom\dropbox\bullet3\demos3\allbullet2demos\GwenTextureWindow.h(28) : see declaration of 'MyGraphWindow'
9>..\..\Demos3\AllBullet2Demos\GwenTextureWindow.cpp(81): warning C4099: 'MyGraphWindow' : type name first seen using 'class' now seen using 'struct'
9>          ..\..\Demos3\AllBullet2Demos\GwenTextureWindow.cpp(8) : see declaration of 'MyGraphWindow'
These changes fix the linking errors, and the program now runs.