After installing TFS 2010, in order to connect to it from VS 2008 or 2005, you must install the Service Pack 1 Forward Compatibility Update for Team Foundation Server 2010. You can download the 2008 version here, and the 2005 version here. Note that you have to have Service Pack 1 installed before you can apply the update.
Once the update is installed, you need to disconnect from the old TFS 2008 (even if 2010 is on the same server) and reconnect. The server name should be entered in this format: :8080/tfs”>http://