We have published the SvnBridge project at http://www.codeplex.com/SvnBridge
SvnBridge is designed to allow using TortoiseSVN with Team Foundation Server. It works by emulating a Subversion server and converting the calls to the TFS API. SvnBridge works as a task tray application that you run on your developer workstation and pointing it at the TFS server, and then pointing your TortoiseSVN client at the SvnBridge running on your local machine.
SvnBridge is still under active development in a early alpha stage. Please check out the project and tell us what you think!