First, you need to download
Once you install everything, you can try adding Team Foundation Server 2010 as destination, but you will be greeted with error "TF31002: Unable to connect to this Team Foundation Server …". Reason behind this is that old Team Explorer 2008 does not know anything about collections.
Solution would be to add it as full path (e.g "http://server:8080/tfs/collection"). I could not do it because every time I entered full path, I also got error "TF30335: The server name cannot contain characters ‘/’ or ‘:’ …". Since official way would not work it was time to come up with alternative.
In order to add TFS 2010 server, you will need to exit Visual Studio 2008 and go into Registry editor. Find key "HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\TeamFoundation\Servers" and at this location just add string value. Name of this value will be what Team Explorer 2008 will use for display. It’s value is full address of your server. It should be something like http://server:8080/tfs/collection.
Now you can go into Visual Studio 2008 and Team Explorer will have new entry. As you work with it, you will notice that not everything is "bump-free" (e.g. tasks). However, source control it self will work perfectly and that was enough for me.