I have created a project in Visual Studio 2008 Professional Edition.
This project contains one .cpp file for each assignment like this...
[-]Source F
You can't have 2 functions called main() in a single project. What you should do is change the names of the functions, and then call them from a new main() function which would function as a menu.
If you make them separate projects, you can switch which one to run with Solution Properties -> Startup Project.