Are you logged in as a standard user? Try cancelling the CD autorun dialog, navigate to the setup.exe file on the CD, right click, then select Run as Admin. It'll prompt you for the admin username and password, enter those and you should be good to go.
Another way is to enable the builtin administrator. Heres how. Built-in Administrator Account - Enable or Disable
Now, logon as admin, then install Office. After finishing, disable the builtin admin again.