You can't install Internet Explorer 7 on Windows 7 as that would mean downgrading the version of IE that Windows 7 has by default (IE8), and downgrading it is not possible.
Furthermore, there is no download of IE7 available for Windows 7 anyway.
Downloads of IE7 are available only for Windows XP or Windows Server 2003.
If you don't like IE8 or IE9, consider switching to either Mozilla Firefox or Google Chrome. My browser of choice is Chrome now that it has all the features I need: