Explorer 9 update problem?

am trying to update my explore 8 to 9 but every time i do a box pop up saying (setup doesn't support the windows service pack version currently unstalled on your computer.Go online and install the required update, then return to the internet explorer installation page and run setup again) but i download the right update i picked the one that said Internet (Explorer 9.0.8112.16421 Windows Vista 32-bit) and that is my computer windows vista 32 i cheked but the update just keeps saying the same thing can someone help me out