The term 'undeclared identifer' refers to some type name, variable name, or #define that the compiler hasn't seen the declaration for. You're either missing a #include, or the identifiers you're referring to don't exist.

Are you including <Cg/cg.h>? If so, what version of Cg do you have installed? According to the documentation, the API you are using was introduced in 2.0. Make sure you're using Cg 2.0 or later.

Do you have more than one version installed? In your screenshot, your include directories look wrong - you have .lib file paths where you should just have include folder paths. Also, your lib paths seem strange - usually Cg installs stuff in it's own folder, such that you'd have to add the include path "....../Cg/include" and the lib path "....../Cg/lib".

Make sure you find the folder where cg 3.0 was installed (inspect any version-related files to be certain), and add the appropriate lib and include paths. The "Library Directories" tab should look like:

...
"<path to cg parent folder>/Cg/lib"

and your "Include Directories" tab should look like:

....
"<path to cg parent folder>/Cg/include"

Edit your include path so that the last Cg is excluded - it should just be:
C:\Program Files\NVIDIA Corporation\Cg\include

You'll still have to add the Cg libs to your linker parameters -
C:\Program Files\NVIDIA Corporation\Cg\lib\cg.lib, etc (or just cg.lib, since you have the library path set up).

Also, make sure that you don't have any global Dev C++ settings that have Cg include paths. The fact that you're not getting errors on #include <Cg/cg.h>, even though you don't have your include path set up properly, tells me that Dev C++ must be getting an include path from somewhere else. Look in the Dev C++ settings (not the project settings), and see if you can find any include paths, etc. Get rid of any that are Cg-related.

Working with include paths, and lib paths, and all that stuff for third party libraries can be pretty frustrating at times, but don't give up. Just make sure that when you get it working, you take notes, so you don't have to go through all of this trouble again.

Still no luck. Followed your advice. No luck. Do you happen to have a working example of cg setup in a Dev-Cpp file for eg.?

I do not, sorry. To test the suspicion of incorrect include paths, try changing your #includes to refer to the complete path of the files, e.g.:

#include <C:\Program Files\NVIDIA Corporation\Cg\include\Cg\cg.h>

Do this for every Cg-related file that you include. If the compiler still complains about undeclared identifiers, something else must be wrong.