[Flash MX] 3D Depth Sorting

I am trying to figure out an algorithm that will give me the perfect depth for polygons being display in a 3D graph. First off, what is the range of depths? From just test it out, I have found that they can not be negative? But was is the maximum? Anyone have prior experience with trying to figure a usable algorithm. All the ones I have come up with end up producing the same depth for different polygons which makes the previous one disappear.