Centralised backups, drive extender and media streaming are not built into Windows 2008.
http://en.wikipedia.org/wiki/Windows_Home_Server gives a nice overview with some details of Windows Home Server - most of those features are not available in Windows Server 2008 but could be added, at significant cost and effort compared to Windows Home Server.
Windows Home Server is based upon Windows Server 2003. If you only want to do light sql services and svn then you could run this on Windows Home Server but it's not supported and you have to be aware of some of the problems you can run into using drive extender with files that are to remain open for long periods.
http://www.klopfenstein.net/lorenz.aspx/setting-up-subversion-svn-on-windows-home-server setting up SVN on windows home server
See this post about running SQL on Windows Home Server
http://social.microsoft.com/Forums/en-US/whsdevelopers/thread/07e2a3e5-a43d-4bd0-8d46-be8ef127861d/ some Add-Ins utilise SQL Server - such as MyMovies.
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