From Microsoft's Internet Explorer FAQ:
Q. Does Internet Explorer 6 Service Pack 1 (SP1) include Internet Explorer?
A. Yes. Internet Explorer 6 SP1 is the most recent update to the Internet Explorer technology, and it includes a full installation of Internet Explorer 6. The service pack is the latest update to the Internet Explorer technologies representing general improvements to Internet Explorer 6. The service pack also includes all prior updates, as well as enhancements to security- and reliability-related technologies.