Screenshot
http://img528.imageshack.us/img528/2379/acd001zw6.png
EDIT:
Okay this seems really strange but it's happening every time so it must be the cause. It seems that if you "hit" or "damage" a wall enough times with a target-at-distance magic spell it brings this minimap up - I was originally testing to see how much I could cast without crashing the game. I've tried a variety of spells and it doesn't seem to work with Wanderlight (which does no damage) or Firestorm (which is area effect). It seems to work best with cheap/quick magic like Fire Dart (with which I usually have to spam my power bar empty twice for the minimap to show up.
Here's another screenshot (2nd level of Dagoth Ur)
http://img529.imageshack.us/img529/440/acd002sk7.png
The game will ALWAYS crash (for me at least) shortly after the map comes up.
I can actually see myself (purple dot) moving as I move. Was this maybe an intended feature that was removed? Or a cheat-code (since the map is fully explored) that was never properly implemented?
EDIT - It works in towns too and citizens show up as orange/yellow dots...