Image half tranperency

To do that open the image you want to make transparent, and the image you want to use as background.
Copy and paste the image you want to make transparent on top of your background image.
Select the Rectagular Marquee Tool. At the top Tool tip under the "Filter", you'll see the Feather property. Change it to 10px and select the hole image that will be transparent. Now go to Select->Inverse.
You'll notice that only the corners of your image are selected.
Select the Eraser tool and erase the corners.
Note that the more Feather you use, the more area is selected and more smoothness you can have in your selection.