This is an extract from the MSDN news letter. Any ideas about the service pack contents?

MICROSOFT VISUAL STUDIO 6.0 SERVICE PACK 4 RELEASE
This service pack addresses customer issues across the range of Visual Studio 6.0 tools, and is a superset of Visual Studio service packs 1, 2, and 3. It is available for free on the Visual Studio Web site as either a download or a CD order. As with all service packs, we recommend that developers creating apps with Visual Studio 6.0 install the VS SP4 prior to releasing their applications.
http://msdn.microsoft.com/vstudio/sp