This is very basic... but I completely forgot how to fix this stupid problem in MSVC++ 2010 Express.
I have a new project, and I added sub-folders in my project directory:
IE. "Headers", "Source", "Resources"
By default, the project requires all the files to be in the same directory as the (.vcxproj) files.
Where in the settings was it to allow/include those sub directories?
Else, I'm forced to do something retarded like this for everthing:
VS2010 lets you create 'filters' in the IDE itself rather than alter the actual project directory. This allows for quick organization in the IDE, but not on the disk itself. If you want to physically put the files in different folders, then you'll have to set these directories up in the "Include Directories" in your project settings.