I downloaded the beta of Office 2010, but wanted to go with the 64bit version, since one exists. 64bit Windows 7 deserves a 64bit Office.
My main concern since an upgrade is not possible from 32bit to 64bit was that my Outlook account wouldn’t be kept. To make sure I had a backup of it I exported the profile from registry:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\Outlook
I didn’t bother backing up any files, since everything is on the Exchange server.
My next step was to uninstall Office 2007, did a reboot, and started Office 2010 installations. Did a reboot, started Outlook and it all worked. The registry key had not been removed upon uninstalling 2007, so Outlook 2010 detected the profile and used it without any work on my part.
Conclusion is that you can just uninstall 2007 and install 2010 and keep your Outlook settings. But it never hurts to backup your outlook registry key just to be sure.
I had trouble activating but found a solution at http://blog.hznet.nl/2009/11/having-troubles-activating-office-2010-beta/.