Transparency issues in openGL

Hey maxers,

Rookie-time! I wanna make a patch where the transparency of two openGL objects varies. So I need to have both objects semi-transparent but also depth enabled, so that the closest one is always rendered on top of the other. While I have accomplished this by reading up on some old threads, one problem still remains: When two objects with blend_enable turned on overlap each other, such that on is in front of the other, the one in the back stays visible (as seen in the first picture). I realise that this is because of the rendering order - but how do i fix it? I tried turning the depth_enable on, but then the object in the back disappears, even when the object in front is transparent (second picture). I've posted a picture of all the attributes, that the two gridshapes has (third picture) - can someone point out, what I am missing? I'm sorry if this has been posted before. I haven't been able to find it...

Thank you!