Review the Team Foundation System Migration Toolkit Spec
The Team Foundation Migration Toolkit specification is available for review here (there are links to leave feedback in the doc). The purpose of this toolkit is to help developers write converters from other version control and work item tracking systems to TFS. The toolkit will also helps if you need to mirror or keep the two systems in sync. Many customers gradually move to TFS, so they need to keep changes synchronized between TFS and their existing systems.
We want to remove all adoption barriers. Often the biggest adoption barrier is transitioning from the existing system to TFS. The toolkit is based on our years of experience migrating and mirroring our internal systems as well as the SourceSafe converter.