When installing a new version of any software over a beta version you should always uninstall the beta software first. Even if conversion from beta to final software is supported it’s a wise precaution to start from a clean slate.
Uninstalling Office 2007 Beta 2 and installing the final Office 2007 is painless (as it should be) with no re-booting required on our Windows XP machines.
That only applies to converting from a beta version to the final release. Upgrading from earlier non-testing versions of Office to Office 2007 works fine – as it should.