In Visual Studio 2005, solution folders improve the manageability of solutions that contain a large number of projects.  You can group projects within the solution into these solution folders. 

However, just having a project hierarchy isn’t enough.  Users of very large solutions may want to hide large portions of the hierarchy completely.  Hiding is different than unloading, because with hiding, you will still be able to keep your project-to-project references when building.

To hide a solution:
1. Create a multi-project solution (project-to-project reference optional, in case you want to verify it builds)
2. Right-click on the solution node, and select “Add – New Solution Folder”
3. Drag and drop one of the projects into the solution folder
4. Right-click the solution folder and select “Hide Folder”
5. Build (in case you want to verify it builds)

To unhide a solution folder, go to the Solution Explorer toolbar and press the “unhide folders” button.