WSS 2.0 SP3
"Microsoft Windows SharePoint Services Service Pack 3 (SP3) contains stability improvements and performance improvements. Some fixes that are included with Windows SharePoint Services SP3 were previously released in separate updates. Windows SharePoint Services SP3 combines the previously released fixes into one update."
Download and Installation Instructions (remember it goes on all servers with WSS code on them)
There is also a language template update for SP3
SPS 2003 SP3
"Microsoft® Office SharePoint Portal Server® 2003 Service Pack 3 (SP3) represents a major evolution in security for SharePoint Portal Server 2003. It further hardens SharePoint Portal Server against potential attacks and other security threats. This service pack also includes fixes that have been previously released as separate updates for SharePoint Portal Server 2003. "
Installation Instructions and Download
"Included in this Service Pack
This service pack includes significant new security updates. This service pack also includes updates previously released for SharePoint Portal Server 2003:"