I have been following Nebraska's practices and have been wondering how our running backs are doing.   The available media like Husker's HQ and huskers.com have chronicled Rex Burkhead to a fault, so I know Burkhead is having a good summer preparing for game with Chattanooga - Tennessee on Sept. 3.   Still, I was wondering how our other backs were doing.   I have seen a little bit on the blue chip recruit Aaron Green from Texas.   How is big Collins Okafor?   I have it in the back of my mind that this guy as force to be reckoned with.   6-0, 230 with good speed.   I'd like to see his power assist Burkhead.   How are the other backs besides the talented Burkhead doing?   I have heard very little.