That is the same website I use as well. This one is good too for Music and games.
http://www.htbackdrops.com/I can take no credit for the menu items with the blue reflections, they are not my creation. Those are from Baddabings modern metal skin. I too wish I had that kind of graphics skill. I plan to use this skin with a remote so it would be cool if I could get those to dim some when not selected and then when they are navigated to they highlight so I knew which menu item I was at, other than by the background image. I am not sure I will keep them there or change them to just words we'll see how a few other ways look.
As for randomizing the images, they are random. Right now it is just one set of images for all the buttons as a test. I have a folder with all the fanart in it. I made a fanart database set up like the pictures database. I created a category for fanart also and just put it on a non used page. Then each menu item unhides a text box that shows an image category>fanart>randomcover> might not be the best way but it seems to work well. eventually it would be set up so each menu item is tied to its own set of pictures. Music Art , Movie art, TV Art, etc. So it is random each time Xlobby loads, not everytime you enter the page.
Someone with more skill and better knowledge of plugins can probably set this up to be random each time you enter the page or maybe change after a certain amount of time.