Don't install 64 bit viewer on 32 bit OS

indra/newview/installers/windows/installer_template.nsi

@@ -35,6 +35,14 @@ RequestExecutionLevel admin	; on Vista we must be admin because we write to Prog
 
 %%GRID_VARS%%
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Alows us to determine if we're running on 64 bit OS; ${If} macros
+!include "x64.nsh"
+!include "LogicLib.nsh"
+
+;; are 64 bit binaries packaged in this installer
+%%WIN64_BIN_BUILD%%
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; - language files - one for each language (or flavor thereof)
 ;; (these files are in the same place as the nsi template but the python script generates a new nsi file in the 
@@ -664,6 +672,12 @@ FunctionEnd
 ;;  entry to the language ID selector below
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 Function .onInit
+!ifdef WIN64_BIN_BUILD
+    ${IfNot} ${RunningX64}
+        MessageBox MB_OK|MB_ICONSTOP "This version requires 64 bit operating sytem."
+        Quit
+    ${EndIf}
+!endif
     Push $0
     ${GetParameters} $COMMANDLINE              ; get our command line
     ${GetOptions} $COMMANDLINE "/LANGID=" $0   ; /LANGID=1033 implies US English

indra/newview/viewer_manifest.py

@@ -461,6 +461,7 @@ class WindowsManifest(ViewerManifest):
                 "%%INSTALL_FILES%%":self.nsi_file_commands(True),
                 "%%DELETE_FILES%%":self.nsi_file_commands(False),
                 "%%INSTALLDIR%%":"%s\\%s" % ('$PROGRAMFILES64' if self.is_win64() else '$PROGRAMFILES', self.channel_oneword()),
+                "%%WIN64_BIN_BUILD%%":"!define WIN64_BIN_BUILD 1" if self.is_win64() else "",
                 })
 
         # We use the Unicode version of NSIS, available from