Well, just because you have a 64bit OS, doesn't mean you have a 64bit version of Office. Even if you have a 32bit of Office 2010, Windows 7 can run the program using WoW64. To check and see which version of Office 2010 you have simply open any Office application. Open the File menu, and then select Help. On the right side, you’ll see information about your version of Office. It will show the suite version and included applications, as well as your precise version number and product ID.
Office 2010 is the first version of Office with a native 64 bit version, but by default, most users will be running the 32 bit version of Office 2010. The default setup for Office 2010 will install the 32 bit edition even on 64 bit systems so you can easily run older addins and VBA scripts for Office. The 64 bit version does let you use larger files, such as spreadsheets larger than 2Gb, but doesn’t offer many advantages for average users.