The post about called criticals is going to be the new foundation for my called shot rule. To aim at a specific location, make a standard attack roll vs. the target's armor class, for torso, limbs and head; if the location is a vital organ or vulnerable point, use AC 5 (half of AC 9, per the rule about halving AC for small targets) or the actual armor class, whichever is more difficult; for really small locations, like an eye, use AC 3 or the actual AC.
On success, the defender takes cuts or bruises to that location, and if it is a called critical (target number +4, or natural 20,) that location is crippled. Using edged weapons severs limbs or the head, pointed weapons causes loss of eyes or organs. Losing a vital organ (heart or brain, for example,) or severing the head means instant death. Otherwise, crippling injuries prevent use of the affect location until healed. If the ribs or half a defender's legs are crippled or lost, the defender is at Move 3 and -1 to actions.