Prepare Windows for 2.1 beta 1:  installer dialogs and bump "build number".
diff --git a/PCbuild/BUILDno.txt b/PCbuild/BUILDno.txt
index 34a9ffa..7de90bd 100644
--- a/PCbuild/BUILDno.txt
+++ b/PCbuild/BUILDno.txt
@@ -33,6 +33,8 @@
 
 Windows Python BUILD numbers
 ----------------------------
+  11    2.1b1
+        28-Feb-2001
   10    2.1a2
         1-Feb-2001
    9    2.1a1