Photoshop :: Mask Fading And Transparency

pictures of my car and adding effects and making my pictures really look good. I am in the process of making a new background for my computer i used a layer mask and set the background image to transparent.. I have the regular picture of my car as layer 1.. now when i use the gradient tool to show the transparency behind it works fine.. i save it as a PNG file and everything but when I go to set it as my background, the BLACK background doesn't fade into the picture.. the surrounding area where the transparent layer was showing through is always WHITE.

how can i make the black fade in? i know i can just make the background of the picture black instead of transparent but i want to be able to post these on the internet and give them to my parents so they can do the same.. so i dont want to make everyone have a black background to make it look right, which is why i want transparent.