It used to be Mechwarrior RPG but now its called Classic Battletech RPG!
http://www.classicbattletech.com/ind...de=full&id=195
Catalyst Game Lab's just released a new revised book or some sort more improved. Its still the same with Battletech since your gonna base your campaign in Battletech History there are also books for that which can be used on both.
I also play the hex based battltech game but only online... got some minis too