agree with Jaxas...
you can create a bounding box for every obstacle like in 82 AUM
if ((((ship_pan.pos_x + 67 >= enemy1_pan.pos_x) && (ship_pan.pos_x + 67 <= enemy1_pan.pos_x + 37)) ||
((enemy1_pan.pos_x + 37 >= ship_pan.pos_x) && (enemy1_pan.pos_x + 37 <= ship_pan.pos_x + 67)))
&& (((ship_pan.pos_y + 67 >= enemy1_pan.pos_y) && (ship_pan.pos_y + 67 <= enemy1_pan.pos_y + 37)) ||
((enemy1_pan.pos_y + 37 >= ship_pan.pos_y) && (enemy1_pan.pos_y + 37 <= ship_pan.pos_y + 67))))
if you are still not frighten :D, just download and see by yourself here
http://www.conitec.net/english/gstudio/aum.php (the laast one)
but it would be more simplier to make a 2d game and make camera to see at the level from the top(look at the 81 Aum, as i remember)
believe it 
