Dude,
In case if one has lost his own key, call up MS and will give you it.
Just make sure you have all the following you call up a MS Rep.
1) The product CD-ROM
2) The computer on which you want to install Office
3) The readable parts of your original product key (if available)
4) The ProductID information in the registry
Source(Holds good for Office/Windows):
*office.microsoft.com/en-us/assistance/HA011508341033.aspx
Now donn ask me Y i need to call MS when I have 3rd party utilities to gimme the same.