Starting with version 4.0.2 the client supports these new
theme directives.
  #define
The #define directive is similar to that used by C / C++
  programmers with a minor difference. If an INI issues a #include directive and
  the included file issues a #define then after that INI file is finished reading
  the #define's issued in that file will be dropped. However, any #define's
  issued in an INI file which later issues another #include then those defines
will remain intact for all sub-INI files that follow.
Download the Examp-MultiMute to see a more advanced version
of these techniques.
See Ventrilo-Theme-Specs.PDF for more details on how these
features work.