In the '80s, Parker won fame as half of TV's ''Simon and Simon'' (he was the Stetsonless blond). But his interest in acting waned after he was shot by a neighbor in 1992. ''I would read scenes involving shoot-outs, written by men who knew nothing about the reality of guns or shooting or being shot, and rage would start to roil inside me like food poisoning.'' Struggling with a crushing depression, Parker retreated to rural California, where his heartrending story picks up. With false starts and apprehension, his ballad of emotional triumph mirrors the endless cattle drives or smelly horse foaling he charmingly illustrates. Peppered with inventive simile and playful self-deprecation, ''Cowboy'' is equally fulfilling.