We are working on an update for Visual SourceSafe 2005 to make it work with VS 2008. We had originally planned to have it available at the same time as VS 2008 downloads went live but we hit a last minute bug that is taking a little time to work out. Our current expectation is that it will be available in mid December. I will announce it as soon as it is.
In the meantime, if you need to use SourceSafe with VS 2008, there is a CTP of the update available – although it requires one manual work around for during installation. You can read more about it on Richard’s blog here: http://blogs.msdn.com/richardb/archive/2007/11/19/vs-2008-users-remember-to-download-the-sourcesafe-ctp.aspx