Is it possible to do per pixel lighting (hardware accelerated or not )without using Nvidia extensions ?
I know Doom 3 has lighting effects like those achieved with Direct3Ds pixel shader, but is it possible to do that hardware accelerated with OpenGL ? and so that it can work with all video cards not only Nvidia (all demos Ive seen use Nvidia proprietary extensions )
Most per pixel lighting effects make use of register combiners of nvidia graphics cards. The same effects can however be implemented by using the ARB_texture_env_* extensions.
I think you will probably be interested in the ARB_texture_env_dot3 extension in perticular.
Where can i read about this extension and it`s use in lighting ?
Check out http://www.paulsprojects.net/tutorials/simplebump/simplebump.html
There’s an implementation of a bump mapped torus in combination with per pixel lighting.
N.
Also, a detailed explenation of the extensions can be found at
http://oss.sgi.com/projects/ogl-sample/registry/
Lots of reading fun 
N.