There's no such thing as installing any products without a
license key. If there's no license key, chances are, it's part of
the installer.
MS products use the Windows Installer to install stuffs. One can
create a specific XML file, use a specific switch which calls the
file to enter the CD key in automatically, thus it appears that
there's no CD key needed. The XML file may also be able to run the
install silently, or partially silent (let you choose installation
location, after that, everything is auto).
By the way, if this version exists, then it's probably the only
version that needs no activation or checking. Not too sure if
Enterprise version needs to activate, but Enterprise version will
be checked regularly against MS servers to see if it's legal.
Starting from Vista and Office 2007, volume licensed products
are checked against MS servers... pass first time doesn't mean you
will pass the second time.