Open the solution in Visual Studio

Right-click the project or solution node in the Solution Explorer.  Choose the Add to Vault Professional menu item.  If you do not see the menu item, then verify that you have already configured the Enhanced Client as the default source control provider.  

You will get a server login dialog and a repository list. Select the repository. Next, you will be prompted for the location in the repository to put the solution hierarchy.  By default, the solution will be placed in its own folder and each project will have a subfolder created, where it will be placed.  You may enter a name for the solution folder, or delete all characters in the text box to put the solution file directly in the selected repository folder.  Project subfolders will always be created.

In the Add dialog, there is a check box to control the manner in which projects inside the solution will be added.  In the common case, all projects will be placed in the repositories as child folders of the solution’s folder.  In the case where this is not acceptable (if two projects have the same name, for example), use this Preserve Relative paths check box to force the working folder project layout to be copied into the repository.