If you're set on using multiple projects, then Dave has the right approach.  With multiple projects in the same workspace, you can quickly switch between them in the project window: go to File >> Set Active Project.
I would caution you on multiple projects: minimize things that are unique and share files wherever you can.  That way you don't end up having to make the same changes in multiple places.  I would still #define constants to differentiate code, but you could have a small .h file unique to each project and name a unique exe file if you wish.