What is Cg?
http://en.wikipedia.org/wiki/Cg_programming_language
http://http.developer.nvidia.com/CgTutorial/cg_tutorial_chapter01.html
http://nehe.gamedev.net/tutorial/cg_vertex_shader/25002/
Function reference - http://http.developer.nvidia.com/CgTutorial/cg_tutorial_appendix_e.html
examples / tutorials