Hi Ted,
There is no Office version that has ever required the re-entry of the product key before applying an update to an already-registered copy. Insertion of the original installion media was sometime required for earlier versions (eg Office 2000).
I can only conclude, therefore, that your copy of office 2007 is either a trial version - for which the trial license has expired - or is an unregistered copy. In any event, if your buddy sold you the PC without the Office installation media, the implication is that he intended to keep it for himself and that you haven't had a valid Office 2007 installation.
FWIW, if you need any of the manuals for your Dell, you can download them from:
http://support.dell.com/support/edoc...0/en/index.htm
And, if you did indeed have a valid Office installation, the System Restore procedures outlined at
http://support.dell.com/support/edoc....htm#wp1088641 may help.