I presume you mean a headsup display minimap.

Here's a code by Zarthor which I believe will work if your minimap has the same ratio as your terrain and is oriented in the same direction.

Code:
var map_ratio[2]; // saves the ratio from real world coordinates to map coordinates
var icon_pos[2]; // where the icon can be placed on the 2d map (screen position)

var map_size[2] = 1024,768;
var terrain_size[2] = 4000,4000;

function map_startup() //upper right quarter of terrain and screen
{
//  map_ratio.x = map_size.x / terrain_size.x; //may be backwards
//  map_ratio.y = map_size.y / terrain_size.y;
	map_ratio.x = terrain_size.x/map_size.x ; //may be backwards
  	map_ratio.y = terrain_size.y/map_size.y ;
}

function map_CalcIconPos(&_WorldPos)
{
  icon_pos.x = _WorldPos[0]   / map_ratio.x;// - (map_size.x);
  icon_pos.y = _WorldPos[1]  / -map_ratio.y;// -(map_size.y );
//		(vec_set(player.x) + 2000) / 3.90625 = icon_pos.x;
//		(vec_set(player.y) + 2000) / 5.2083 = icon_pos.y;

}

panel player_icon 
{
	bmap = player_tga;
	flags = d3d,refresh,overlay,visible;
	layer = 20;
}

function place_player_icon() //places the player icon on the chart
{
	if(land_chart.visible == on || land_chart_explored.visible == on)
	{
		map_CalcIconPos(player.x);
		player_icon.pos_x = icon_pos.x;
		player_icon.pos_y = icon_pos.y;
		
		player_icon.visible = on;
	}
	
}