http://forum.shrapnelgames.com/showthread.php?t=50616
Get the heightmap utility from the MBT forum and learn to drive it. The height map for the area should be downloadable from the usual sources of geographic data. Googling Kohima, Burma should give you the coordinates?.
That will give you the underlying land contours, and then you need to populate it with the buildings, trees etc as existed then. (Looking at the place on google and cross referring the WW2 sketch maps a Google image search threw up its a lot more built up nowadays - but the main roads basically still match).