|MadSci Network: Physics|
you are right, this "0th Law" exists, but actually it is something you probably don't consider worth thinking about. You have different but equivalent formulations, one of them is:
"The zeroth law of thermodynamics states that if for example you have a Body (A) and a Body (B), both at the same temperature; and then you have a Body (C) which is at the same temperature as Body (B); Therefore the temperature of Body (C) is equal to the temperature of Body (A)."
So, you see, it is quite easy - if A=B and B=C, then A=C! (If you want to be a scientist, you can replace "same temperature" by "thermal equilibrium", but it means esentially the same).
Try the links in the MadSci Library for more information on Physics.