Added command line option for Scons to select which version of MSVS to use.   Versions 7.1, 8.0 and 9.0 are allowed.   Usage is scons MSVS_VERSION=8.0.
diff --git a/SConstruct b/SConstruct
index cd5b228..c1dc624 100644
--- a/SConstruct
+++ b/SConstruct
@@ -50,6 +50,8 @@
 opts.Add(ListOption('winsys', 'winsys drivers to build', default_winsys,
                      ['xlib', 'intel', 'gdi'])) 
 
+opts.Add(EnumOption('MSVS_VERSION', 'MS Visual C++ version', None, allowed_values=('7.1', '8.0', '9.0')))
+
 env = Environment(
 	options = opts,
 	tools = ['gallium'],