I am pleased to say the TFS Migration and Synchronization Toolkit (toolkit) is officially released. You can get it here on CodePlex. The toolkit provides a set of classes and a reference implementation (and a good example) for migrating and/or synchronizing third party version control and work item tracking systems to Team Foundation System. The toolkit makes our lessons learned and best practices available for others to use when writing converters between their existing systems and TFS. If you follow the Team Foundation System blogs, then you've seen Brian Harry's dogfood statistics for Microsoft's internal use of TFS. Well, those changesets and bugs are migrated and synchronized with the systems we used before TFS. This is necessary because our build labs and some of our internal tools have not all been converted to TFS (yet), so we still need the previous systems. Given the volume of users, files, and bugs, we have a great deal of experience with the issues involved in migrating and synchronizing with TFS.
If you download the toolkit, I encourage you to look at the reference implementation that migrates with SharePoint (WSS). This implementaiton migrates documents between SharePoint and TFS version control as well as migrating SharePoint task lists with TFS work item tracking. By following the code in this reference implementation, you will get a good feal of how to implement your own converter from end to end.