NBA LIVE 03
If you want a really good rookie to become even better, put him on a really crappy team, and take any player with ratings above 70 off the team and replace them with players with ratings close to 50. The rookie will try to make up for the rest of the team if you simulate a season.
I had this one guy, last name was Taber, #3 draft pick by indiana pacers, did the above stuff and BOOM! within 2 seasons his overall rating jumped from 85 to 94. Then I screwed around with mods and had to delete all my saved franchises