You probably have an Office 2007 file format compatibility pack installed for Office 2003, and that's what the update is for. What do the details for the update say, or what is the KBXXXX at the end of the update name? You just take whatever the KBXXXX is, run a search for it, and it'll map to a Microsoft Knowledgebase article that will give greater detail for that update.
Is it necessary to update all Microsoft Updates ie: I just received update for Microsoft Office 2007 which I don't have. I have Microsoft Office 2003. Comes in as important update. Not that computer savvy, would appreciate help. I have new Dell w/Windows 7 Professional installed. Thank you.