Here are some tutorials from CausticFX
WWW Link">LinkThe 'Transparent Borders' should help with the logon dialog.
Here is the address for a fun one showing how to make the OSX wallpaper:
http://dr-photoshop.com/tutorials/index.php?id=60
Sorry, I can't seem to add a second link, so just copy the address into your browser address bar.
That should help with creating the additional reflections across the top of the logon dialog - although, those are probably made using a cropped shape, a gradient (white to transparent, or white to black), and some added transparency.
Good luck.