Leading "C:" no longer hardcoded in the default installation directory.
After removing that, two testers on machines where C: is not the system
drive reported that the installer suggested their system drive instead
of C:, and that's what they wanted it to do.
diff --git a/PCbuild/python20.wse b/PCbuild/python20.wse
index 64c3ef0..90ecf25 100644
--- a/PCbuild/python20.wse
+++ b/PCbuild/python20.wse
@@ -203,11 +203,20 @@
 item: End Block
 end
 item: Remark
-  Text=Note from Tim:  doesn't seem to be a way to get the true boot drive, the Wizard hardcodes "C".
+  Text=Note from Tim:  The Wizard hardcod "C:" at the start of the replacement text for MAINDIR.
+end
+item: Remark
+  Text=That's not appropriate if the system drive doesn't happen to be C:.
+end
+item: Remark
+  Text=I removed the "C:", and that did the right thing for two people who tested it on non-C: machines,
+end
+item: Remark
+  Text=but it's unclear whether it will always do the right thing.
 end
 item: Set Variable
   Variable=MAINDIR
-  Value=C:\%MAINDIR%
+  Value=\%MAINDIR%
   Flags=00001100
 end
 item: Remark