It sounds as if you have the wrong version of Office 2003 Install CD that you are trying to use as an activation key.
There are several versions of Office and you'll need the correct CD for the install that you have there. If this is a Prebuilt system the chances are that it came slipstreamed on the original Rescue CD.
If you are a in a place with more than 5 copies of Office running then it's possible that you'll need the Volume License Version of that version of Office.
But to get around this problem you can load the Update Software from the MS Update Web Site and using that it will allow you to update Office without a CD but you'll need to perform the download from the Windows Update site and it will apply the required software for office.
It will be slower but may prove the only way around your problem.
Col