Let us know what you're trying to accomplish with a little more detail.
Do you want the black background behind your actor?
Do you want the text to have the alpha so that it'll be in front of the actor?
If so you can just save a solid black background in photo shop, then put it behind your actor in photo key.
For the text try something that Axeman helped me with a while back.
In photo shop, open a new file.
Add a new "layer" it will have an alpha channel.
select that new layer and put your text on it with whatever color you like. that means when you import it into photo key, only the actual text will be visible.
Delete the first layer, the one without text so that only the alpha layer remains.
save the file after you get it to look how you like.
Now you should be good to go.