Microsoft has released a number of Office 2003 updates today. The most exciting (well, for me anyway) is the release of OneNote SP1. There are also Service Pack 1 releases for the Office 2003 Suite, Visio 2003, and Project 2003.
Interestingly, Microsoft is offering two different downloads for each SP1 release - a full installer (big) and a special installer for those who have their original installation CD at hand (much smaller).
Go to the Office Update web site to determine which updates are available for your system.