By default, the Office 2010 setup will install the 32-bit version regardless of whether your operating system is 32-bit or64-bit. To install the 64-bit version, do the following:
- Insert the Office 2010 disc.
- When the AutoPlay prompt appears, click “Open folder to view files”.
- Open the “x64” folder.
- Run the setup file.
Please see this article for compatibility notes and differences between the 32-bit and 64-bit versions. Office 2010 64-bit is not compatible with Windows XP.