Just wanted to add another way to accomplish this, as I was just about to ask a question regarding this topic and figured out the solution.
If you truly need to bring over the raw user control files into a new project, you will find simply adding them via 'Add -> Existing Item...' will make each file come into the solution independently and not structure them properly in Solution Explorer.
The trick is to open up the (2) associated user control code files outside of VS.NET prior to adding to your solution and modify thier namespace to be that of your new project. So if in the old project your namespace was:
MyOldProject.CustomControls
...you will want to rename in the .cs
and .Designer.cs
to the following:
MyNewProject.CustomControls
Then when you go back into VS.NET add add all of the existing items, they will be in their proper arrangement as follows:
MyControl.cs
-->MyControl.Designer.cs
-->MyControl.resx
-->MyControl