Alpha Channels/ Transparency...HELP!

Hey Guys...

I have a question about transparency and alpha channels. I'll explain what I want to do, and hopefully someone can tell me how. I'm creating an image in a 3d modeling program. I want to export an image file (Targa, 32 bit, with Alpha Channels) into photoshop, then extract the alpha channel(that being the black background in this case) so that i'm left with the actual image of the 3d model over transparency, with which I can use to layer on top of things created in photoshop. Ok, that said, i'll explain it one more way, in hopes to make it clearer. I'm doing weather graphics for a news program, and have rendered out a cloud in a 3d modelling program(3d studio max). I want to import this image of the cloud into photoshop, and layer it over graphics I created in photoshop, minus the background created in the exporting from the 3d program. Any help?! I have tried everything and can't figure out how to mask out alpha channels in photoshop. Thanks alot!

***Justin***

If you are using PS7.0 (all I've used) there is an extract function under filters. Not sure that earlier versions use it. You outline the basic shape of the cloud with the pen and then the paint bucket tool fills it in. When you exctract it should be pretty darn close.

-OR-
If you turn off antialias and have a solid background in max when you render your cloud you can just use the magic wand on the background and delete it. Then use the soften tool to make the jagged edges smooth. Just soften it a little with low opacity.

That's just a couple of the ways you can do it. I usually use the last one because I'm so used to using paintshop pro... (forgive me father I have sinned) But the extract function is great!

just don't turn anti alias off with the magic wand tool....it will then select the black background and still keep the object smoothness.
I've used the magic wand on many complicated objects. also...if the cloud has any transparency...i don't think you can get the background that's on the cloud to change.
another suggestion : load the image you want as a background into 3DS Max and just render the cloud onto that background. thats what i would do.