http://msdn.microsoft.com/vstudio/support/servicing/. I think its kind of interesting that VS2003 didn't have a service pack for 3 years, yet 2005 is having one not even 1 year later. Perhaps because of all the new features that were shipped with this version, however VS 2003 shipped with many new features as well. Since MSBuild is technically a part of the .NET Redistributable, I'm not sure if the service packs will impact anything related to MSBuild. If I find out more I'll be sure to post more.
Sayed Ibrahim Hashimi