I got Office 2003 Pro from a frd & installed on 3 genuine systems, 2 Win 7 64 & 1 XP 32. Installed fine on all the systems & didn’t asked for anything like activation, etc… Works & updates through Windows Updates fine on all the systems.
Why not use Open Office or Libre Office? You would not be risking pirated software and would be compatible with more current MS Office. Libre Office is under constant development.
I think it’s safe to assume that if you got it from a friend and it says that it’s already activated when you install it, then it’s not legitimate… 88)
Only corporate licenses behave this way, and I’m assuming your friend isn’t a corporation.
As rodpal said, just use OpenOffice or LibreOffice (I prefer Libre) and you don’t have anything to worry about.