1) Make a 400x400 document. Now press "D" on your keyboard to reset the foreground and background colors to black and white. Make sure your background is black.
2) Now use the Elipitical Marque Tool
and make a pretty big circle, hold shift to make the circle perfect. 
3) Make a new layer now (do not deselect the circle). Get the paint bucket tool and paint the circle white on the new layer.
4) Now we want to apply the layer style to the white circle. Do this by right clicking the white circle layer and go to Blending Options, apply these options and colors:
5) Duplicate the black background layer so we can modify it.
6) Select the Circle Layer and go to Select>Load Selection and use the default settings for the window, click ok. Now select the duplicated black background and press Delete.
7) Now right click the background copy layer and go to blending options. Apply these settings:
Your done, your Xbox Button should look similar to mine below:
