1) Do NOT Install Medieval 2 Total War in the standard library of C:\Program Files\Steam... In fact, do not install in either Program Files or Program Files x86. The guys at Europa Barbarorum 2 made a great guide (see: 1. M2TW Installation Instructions) on how to install and/or move your Medieval II installation outside of Program Files, whether using Steam or not. Having your Medieval II installation in Program Files has been known to wreak havoc on mods, causing a variety of issues, and as such I cannot help you if you experience bugs or crashes but fail to take this important step.