[OpenGL 2.0] Depth buffer problems

[Brainer]

A i see it if they were on the same level they would collide with each other.

Yes, that's basically what I'm trying to achieve.

EDIT
Or maybe you could tell me how do I bring one sprite on front of the other once it was rendered already? Hm, maybe not the best descriptive way of telling you about the problem, that's why take a look at these two images:
http://i52.tinypic.com/2rff2bt.jpg and http://i56.tinypic.com/2d91qf9.jpg
What I mean is that no matter which sprite I choose, it's drawn on top of the other ones.