Try a right click and then Properties on one of your icons for starting Medieval2. That should identify the directory that M2TW is installed in. Within that directory there should be a directory named "tgas" (which is short for Targa files, named for early frame buffer display boards).

There are lots of available viewing software tools if you only have the vanilla MS picture viewer. I highly recommend Faststone from faststone.org. Be sure to go to the .org address, there are campers on the .com iteration. Might be rebels.