is there anyway i can make it when a halo hits a surface it leaves a red splat on the face of the surface :-? 
Make the spont on the wall from the beginning.
Make for it a new material of the right flavour
Add a Material IPO on Alpha Channel so that alpha is 0 up to the frame when the wall is hit, then 1 from then onwards.
Stefano
Thats a cool idea, S68.
I’ve been doing it like this (if i understood the original post):
Created blood pattern in a paint program, just a splat of blood with the rest of the image black.
Put the texture on the last layer of the wall’s material, and used Col and Alpha in far right (in Textures, press CalcAlpha and then UseAlpha).
Add an Empty, place it where the blood is going to be (in front of the wall)
Back to Materials, Press Object and type Empty in the box next to it.
To turn on from a certain frame onward:
Frame you want the blood the appear = turn Col slider to 0 and press I and select All Mapping
One Frame after that = turn Col slider to full, press I and then All Mapping.
Im not sure if that last part works though.