Here's
one application of ChaosSlayer's suggestion.
This is a quest script that forces new characters to start in a tutorial zone where they must speak to the main quest NPC to progress. That npc identifies the new character's race and class, and let's him know he will be unable to progress any further if he is not an allowable race or class. He then lists the allowable races and classes, and gives the player options for converting to a new race/class.