What is a .POD file? That is a good question! A .POD file is an archive of many seperate files that the MTM2 game uses to make a truck or track. It is similar to a .ZIP file, except that the files it contains aren't compessed. The files it contains for a truck are .BIN, .RAW, .ACT, .TRK and sometimes .WAV. Oddly enough, that's what the other pages in the Files section of this site are about.
A .POD is created using programs like Tracked2 or WinPod. It can then be "mounted" (added to the pod.ini list) for use in the game. It doesn't sound like much but that's all there is to it.