Deleting the old workspace is probably what you want to do. You can do this with the tf workspace command ( http://msdn.microsoft.com/en-us/library/y901w7se.aspx ), but an easier method is to use the free TFS Sidekicks add-on which gives you a GUI to manage and delete workspaces: http://www.attrice.info/cm/tfs/index.htm
Install Team Explorer 2008
Install Visual Studio 2008 SP1 (This will upgrade both VS2008 and Team Explorer 2008 to SP1)
Install VSTS 2008 Forward Compatibility Update
When you create a new soluction (File -> New Project), you will see a checkbox in the bottom right corner to add the solution to source control
Add existing Project:
If you have already created a solution, you can right click on the solution in the solution explorer, then select Add to source control.