Microsoft has made available Office 2010 Professional Plus public beta in both 32-bit and 64-bit versions; however, Office 2010 Professional public beta is only 32-bit. When you visit Office web site and click “download beta” link, you're brought to Office 2010 Beta page, when hove over "Get It Now" button, in upper right corner, you'll see two pop-ups:
For home, small business, and school - Clicking “download” will trigger a download of Office 2010 Professional (which includes Word, Excel, PowerPoint, Outlook, OneNote, Publisher, and Access) in Click-To-Run format, a virtualized environment that sandboxes Office from rest of your PC. This option is still 32-bit only.
For enterprise and mid-sized business - Clicking “download” will trigger a download of Office 2010 Professional Plus (everything above plus InfoPath, SharePoint Workspace, and Communicator) in a "normal" full download that's about 650 MB in size. You can choose between 32-bit and 64-bit versions (supports Vista SP1, Server 2003 R2, Windows Server 2008, WOW, Windows 7.)