Simple.
Make a circle selection.
Fill with a darker off-blue (not pure blue, more like the shade of the forum default skin, only a little darker)
Dodge the bottom part until it looks good
Paste in a windows logo
Use pen tool to select a shape similar to the reflection on the orb
Fill with white
turn down opacity.
Here's a bit I did in photoshop. Download and open it, you will be able to see the layers I made and the effects 'n what not.
http://rapidshare.com/files/227008981/vista.psd.html