If you ever tried to connect Visual Studio 2008 with Team Foundation Server 2010, you ran into a problem. These two aren't compatible unless you do some additional installations. To achieve this just follow the steps bellow.

1.) Install Team Explorer 2008

First, check if you already have this software installed by going to Tools > Options > Source Control. If there is an option "Visual Studio Team Foundation Server", you don't need to install it.
If not, download Visual Studio Team System 2008 Team Explorer from http://www.microsoft.com/en-us/download/details.aspx?id=16338.

2.) Install Visual Studio Team System 2008 Service Pack 1

By clicking on the link http://www.microsoft.com/en-us/download/details.aspx?id=10834 you will download Visual Studio Team System 2008 Service Pack 1 Forward Compatibility Update for Team Foundation Server 2010.

This is an update for the 2008 SP1 version of Visual Studio Team System Team Explorer and allows the 2008 SP1 version to work with the Team Foundation Server 2010. The update will allow teams to move forward and use the Team Foundation Server 2010 server even if part of the team continues to use the Team Explorer 2008 SP1 client.

3.) Final configuration

After you install these two updates, you can try setting Team Foundation Server 2010 as destination. There are some chances you'll ran into some problems...

Problem #1: "TF31002: Unable to connect to this Team Foundation Server...". Problem is that Team Explorer 2008 doesn't know to which collection you wan't to connect. You can add your collection path, but...

... problem #2 is that, when you try to add your collection path as "http://server:8080/tfs/DefaultCollection", you will get another error message like this: "TF30335: The server name cannot contain characters ‘/’ or ‘:’ …".

Solution for this problem is to add it manually, through Registry:

  1. Exit Visual Studio
  2. Open Registry editor (START menu > type "regedit", and hit ENTER)
  3. Find key "HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\TeamFoundation\Servers"
  4. Create string value key, with any name you want (it will be displayed in Team Explorer 2008), but for value set your collection path like "http://server:8080/tfs/DefaultCollection"

Now, you can start Visual Studio 2008, and check the collection path under Team Explorer.
Everything should work fine.

NOTE: because you connect VS 2008 with newer generation of TFS (2010), there might be some compatiblity issues, where VS 2008 won't support some features that TFS 2010 does, but source control will work fine.