Ah ha! looky what I found

Code:
Distance = Radius * acos( cos(Lat1)*cos(Lat2)*cos((Long1-Long2)) + sin(Lat1)*sin(Lat2) )
Ok I've got my distance function... Put simply it uses the great-circle formula to figure it out.

Now... I think what I'm aiming for is to figure out how to get a 2D vector from my current point to the destination point. I'd obviously be updating this vector each iteration of my main game loop to get an accurate simulated curve.


btw, I think that I'm going to stick with knots and lat/long for my co-ordinate system. It'll be easiest for both development and the players to wrap their heads around. (Has worked for hundreds of years so far, right? )