i guess it depends... if you don't know what you are doing it would be difficult!
i don't know much about what the DMPs do day to day, but i would imagine they do a lot of texture projections and use more than just photoshop (definitely for set extensions, i'd imagine thats shake.)
the texture department in film use bodypaint3d and photoshop.
you should post some of your work, gec-t and thx1138 do some pretty sweet paintings, i'm sure they will help you out a bit.
if you missed thx's latest thread its very impressive and... here