Office 2007 is not an update package of office 2003 that you can download from Microsoft update. It is a different version of the software and require a new purchase.
If you would like to know how to get Office 2007, you have come to the right place. We have a recommendation on a free alternative here, with the link for download provided below: http://www.openoffice.org/
It is free to download, updated infinity into the future and forever yours to own.