Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Support for Office 2003 ends April 2014 (that's critical updates and fixes)
Office 2003 is not fully compatible with win8, and you don't mention the win version.
Is your version of Office 2003 a retail version that you purchased separately?
Has any preinstalled Office trial version been uninstalled?
You don't Register Office, you activate it by using the Office Key