This problem can occur with Microsoft Office 2003 when installed on Microsoft Windows Vista. It may also occur with Windows 7 and Office 2007, and Office 2010.

To allow the EULA to be accepted once and for all run regedit

Open the Key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\11.0

Right-click on 11.0 and on the menu that appears Left-Click on Permissions.
In the permissions window make sure that Users have Full Control set to Allow