Jonathan Wanagel, a member of the CodePlex team, has been working diligently on a thing we're calling SvnBridge. The software acts like a Subversion server, but forwards your requests on to a TFS server. This allows you to use familiar tools like svn.exe and TortoiseSVN to talk to a Team Foundation Server.
Yesterday, he pushed the source code out to our CodePlex project. We're working towards a first binary release soon.
The v1 release will be a client-side proxy that runs in your Windows system tool tray. The home page for the project lists the Subversion operations we're intending to support for v1... it's not a complete set, but should be the reasonable list required for common workflow. Scott and I will be helping Jonathan out for a few weeks while we finish the v1 release.
The v2 release will have two versions: an updated version of the client-side proxy, and a version that can run on an IIS server. The server-side version will open up support for non-Windows Subversion clients. Once v2 is done, we are planning to deploy a version of the software for all CodePlex projects (sorry, we don't have a firm timeline for this yet).
Now we can add SvnBridge to CodePlex Client, TeamPrise, and Team Explorer as ways the community can access CodePlex project source code.