Source: http://office.microsoft.com/en-us/p...uestions-HA101674631.aspx#About_Office_2010_4Office 2010 products are available in 64-bit versions; however, for the best productivity and user experience, Microsoft recommends 32-bit Office 2010 for both 32-bit and 64-bit operating systems. Office 64-bit is optimized for advanced data analysis scenarios that most users don’t require, and existing 32-bit add-ins are not supported on Office 64-bit.