I’ve posted a whitepaper from the Office Supportability Group that details what is in Office SP1, which everyone should install if you are using any Office 2003 application.
SP1 is available as separate downloadable patches for OneNote, MUIs, Project Client and Server, WSS, SPS and Visio. Visio’s SP1 download is located here; if you don’t have it, install it. The Visio SP has some important printing and org chart solution fixes, among other updates.
The main Office 2003 SP1 patch, available here, includes security updates for FrontPage, OWC, Publisher and the other core Office applications.
This is a level 300 document and has some good tips and tricks on patch deployment. It also provides insight on the advantages of using the Local Install Source (LIS) for patch management. This whitepaper will eventually get posted to the Office Resource Kit web site, but you can check it out now if you are trying to decide whether or not to upgrade.