I''m trying to do a shadow casting demo, but at a certain moment in my program i need to know where a light is relative to my object coordinate system. I tryed it with glGetLightfv(GL_LIGHT0, GL_POSITION, etc.) but it returns the position relative to the world coordinate system. Is there a function that returns what i want it to return, or i''ll have to use an inversed matrix? I tryed it also with an inversed matrix, but it doesn''t work. Anyone can help me?

Use that inversed matrix, it''s actually easy to implement than you thing. Or you can learn 3d matrix math, edit that matrix as you would the modelview matrix, and apply those changes to the light coords.