Re: How do you get blood decals to apear on dead npcs?
If you are comfortable with C++ reviewing the Source SDK code may help a bit.
Mods can be built on the Source engine to allow for projected decals that aren't currently supported.
In Source there are two types of ragdolls, dead NPCs and ragdoll props, each with a different collision system.
Level designers can also use the env_blood entity to project blood onto ragdolls, which is represented by class CBlood, defined in effects.cpp.