I'm not sure what the problem is with the game freezing. What I can tell you about the car chase is that you need to chase the culprit in your car for a while.
After you've followed him/her long enough, Nancy will say something about the culprit going to the railroad. When Nancy says that, forget about following the culprit and head to the railroad station as fast as you can.
Maybe someone else will have a suggestion about the game-freezing problem, or you could post a note about this problem in the Glitches forum.