That's the risk with a beta. They concentrate on functionality, not on (un)installability. Now report it as a bug, and continue with an older version of Office until this is resolved.
A few days ago I had a problem with the Outlook in Microsoft Office 2010 beta. When I reinstalled the program, something went wrong and it would freeze at a point in the insallation process, and never would open my .pst file.
I tried fully uninstalling Office, but this did not solve the problem. I tried repairing it with the installation program, and this did not help. There seems to be something left on my computer that is stopping the install. The Microsoft web site does not help with the Office 2010 beta, and am really stuck.
I have a couple month old Toshiba 64 bit system running on Windows 7 64 home edition.