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.
http://www.intrinsia.net
hope this can be of use :)