To install 32-bit version:
Office installs the 32-bit version automatically even if your computer is running 64-bit editions of Windows. You might want to install the 64-bit version of Office if you usually work with large databases or worksheets.
To install 64-bit version:
1.If you ran Office Setup from the root folder, and you clicked Customize, click Close to exit Setup.
2.Click Yes to cancel Setup, and then click Close
3.Go to the x64 folder on the Office disc, and double-click Setup.exe to run the 64-bit version of Setup.
Your computer must be running at least 64-bit edition Windows 7 to install 64bit version.