The 64 bit version of Windows 7 comes with both 32 bit and 64 bit versions of IE 8. By default the 32 bit version will be used. If you upgrade to IE 9 on a 64 bit version of windows 7 you have to install the 64 bit IE 9 installer, which installs both the 32 and 64 bit versions of IE 9. The 32 version of IE 9 will still be the default IE used.