So I just uploaded a tutorial outlining the basic procedure using camera mapping for painting mattes and then projecting them back onto your geometry. All in all it's a relatively basic tutorial but it will give you some basics so you at least know how to set it up in Max and your paint package. Further down the road I plan on doing another in-depth tutorial that explores more of the camera mapping features in Max. For the time being this first tut can be found in the tutorials section of my site.
hope this can be of use :)