He is a mercurial player, but the one thing that has improved consistently (not that it's great) is his defense. He seems to have learned to cut off angles much better and really tends to stay between the offensive player and the hoop fairly well (unless he switches to a faster guy). Once he is between his guy and the hoop, his size works well to intimidate just enough.
Offensively in the lane Rollie, you are spot on -- clumsy and unconfident. Sometimes, I think he forgets that he has a height advantage on most guys who cover him and I think he fears that his deficits in speed and quickness will cost him. When in the lane, he needs to use the other players strength his own advantage -- drive hard and get them engaged, then stop and pull up -- he has 5-8 feet wide open I think just about always -- no one can block the Dirk short range fallaway. Once they start to cover that, it will open the lane more. With that said, he's been driving more -- and perhaps with some success, he'll get more comfortable. The problem with him has always been that once he experiences some hardship (loses the ball; gets stripped; misses the shot....), he gets quickly gun-shy.