If you are using Visual Studio 2005 (along with Team Explorer 2005) to access Team Foundation Server, an update patch has been released that will allow Team Explorer 2005 to communicate with Team Foundation Server 2010.
In general, after installing the update patch, you will be able to use Visual Studio 2005 to access legacy (2005) TFS servers as well as TFS 2010 servers. If you switch to a TFS 2010 server, you will be able to continue using the basic functionality of TFS but will not be able to utilize new TFS 2010 features (e.g. Branch Visualization, creating new Team Projects, etc.) - you must use Visual Studio 2010.
Also, when connecting to a TFS 2010 server, you will need to enter the full URL for the TFS 2010 Team Project Collection – e.g. http://TFS2010Server:8080/tfs/CollectionName.
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