While there are projects like LizardTF, IMHO you're better off running SvnBridge and then using your real SVN clients.

SvnBridge allows you to use TortoiseSVN and other Subversion clients with Team Foundation Server. It converts the calls made by your Subversion client to the API supported by TFS.

SvnBridge works by running an executable on your local machine that acts as the bridge to TFS. You point SvnBridge at the TFS server, and point TortoiseSVN at the bridge running on your local machine. This allows you to use TortoiseSVN with any TFS server without needing to change the TFS server in any way (no need to convince your system administrator of anything!).

The only drawback (and it's a very small one for what you get) is that you currently have to download and run the software locally, and then point to localhost:8081 (or whatever port you decide) as your server.

I've asked the CodePlex team to host it themselves to remove that barrier, but I'm not sure when/if they'll be able to get to that.

While I personally prefer our interfaces (VS, tf.exe, etc) most of the time, I'm sure there's also value in SvnBridge for developers that like/prefer their existing SVN clients (be it svn's command-line, or TortoiseSVN, or whatever) but want/need to interact with TFS.