Some companies deploy office 2007 providing a customized setup, encoding the license key, via a .MST file.
Users typically have to install using a command like:
setup.exe /admin File.MST
The install wizard does not seem to accept any argument, but there is an easy workaround: you just need to copy the installation tree to a folder where you have write permission and to copy the .MST file in the Updates folder. Then you run the installation without specifying any argument. The setup automatically looks for MST files in the Updates folder.