If you are using Windows Vista:
Go to Control Panel --> User Accounts and turn-off User Account Control.
Restart your computer, start an Office program, accept the EULA, restart an
Office program to make sure EULA doesn't pop-up, go back to User Accounts
and turn User Account Control on, then restart your computer once again.
Otherwise:
You must accept the Office End User License Agreement
every time that you start an Office program:
http://support.microsoft.com/kb/884202/en-us