Help me customize my desktop in Windows 7

I can’t change my background in Win 7 starter. I think Windows 7 doesn’t support changing of background and theme. Is there any other way to do this?
I want to customize the look of my computer desktop, change the background picture and themes. I’ve seen a laptop somewhere in the shopping mall, I’m not sure what kind of OS there using but I think it was a Windows 7 version. It was really amazing, when you click on the windows start orb a butterfly will appear and keeps flying on the Windows for a couple of seconds and after that it will land somewhere the Windows start orb.
Does anybody know how they did this ? I really want to customize my desktop. Please help me with my desperation.
