If you have an MSDN or TechNet subscription, currently, two downloads are available at each site: 32-bit (x86) and 64-bit (x64) versions of the Professional Plus Retail edition. Subscribers to each service get a single product key for the Office 2010 download. If past history holds true, this key can be used to activate two copies: one on a desktop PC, the other on a portable PC that is used by the same person as the desktop PC.
Anyone considering an Office 2010 deployment should be testing both the 32-bit and 64-bit versions. But if you’re planning to use the software in production environments for normal business use, I strongly recommend installing the 32-bit version, even on 64-bit Windows installations? There’s no real advantage to using 64-bit code unless you expect to work with very large Excel files, and there are potentially substantial compatibility headaches caused by add-ins that aren’t 64-bit aware. Microsoft agrees:
This additional memory capacity is needed only by those Microsoft Excel users who require Excel spreadsheets that are larger than 2 gigabytes (GB). The 32-bit version of Office 2010 provides the same functionality and is also compatible with 32-bit add-ins. Therefore, the 32-bit version of Office 2010 is installed by default.
Normally, subscribers get 10 product keys for this retail SKU, plus an additional key for use on Volume Licensing copies. A notice at both MSDN and TechNet Microsoft says additional product keys for subscribers will be available on April 30.
Office 2010 also provides support for 32-bit Office 2010 applications that run on 64-bit Windows operating systems. Office 2010 lets users continue to use existing Microsoft ActiveX Controls, Component Object Model (COM) add-ins, and Visual Basic for Applications (VBA), which are primarily 32-bit because no 64-bit versions are available yet for many add-ins. Supporting 32-bit Office 2010 applications that run on 64-bit operating systems allows for better compatibility with controls, add-ins, and VBA.