Clarify winsound.beep docs, in response to c.l.py beep brouhahalet.

Doc/lib/libwinsound.tex

@@ -21,6 +21,11 @@ two functions and several constants.
   through \code{0x7fff}).  The \var{duration} parameter specifies the
   number of milliseconds the sound should last.  If the system is not
   able to beep the speaker, \exception{RuntimeError} is raised.
+  Note:  this function works as documented above only on Windows NT and
+  Windows 2000.  Under Windows 95 and 98, the arguments are ignored;
+  if the system has a sound card, the system default sound is played
+  (typically ding.wav, or whatever is registered as the default sound via
+  Control Panel -> Sounds); else (no sound card) the standard system beep.
   \versionadded{1.5.3} % XXX fix this version number when release is scheduled!
 \end{funcdesc}