Did your system come with a 60 day trial or the full version?
My machine came with a Student/teacher version trial version and key for the
trial version (the trial version won't work without the trial key as far as I
know)
If you have kept all the disks/papers etc that came with the machine in a
safe place, then there should be a piece of paper with details of your
microsoft pre-installed software. including keys needed to install stuff. In
my case it had encarta 2004, works7/money 2004 as well as office 2003 S&T
(trial)details on it.
Never bothered with it as I have 2003 pro though.