One of the great features in Visual Studio is the ability to startup more than one project at the same time. You do not need to create two solutions, for example, for a client and a server to be able to debug them both.
I thought everybody knew how to do this, but when I found out that two members of a project team I am working with did not, I decided to blog how to do this.
Select the solution in the Solution Explorer, right mouse click and you will see the following menu:
Select the Set Startup Projects menu item, and a property page will appear that lists all the properties in the project. For example:
You can associate an action with each of the projects: None, Start, or Start without debugging.
When you start execution, the projects that you wanted to startup will begin execution. If you allowed debugging, and set breakpoints, the debugger will stop at the appropriate places.