The question is, what type of .mdl are you talking about?
I can list 3 types off the top of my head. WC3, NWN and Half-Life all use models with a .mdl extension, but all three are different and won't work with each other. A NWN .mdl, the only type I've had experiance with aside from WC3, is FAR different from a WC3 style one