Also it would help if you actually signed up, instead of using Bugmenot's site where you can get login username's and passwords. Anyway, you need to design it first with any Photo editing software, free ones are Paint.NET, and GIMP, there maybe some other but them ones are the ones I have had experience with, then you need to cut them up and then use a program such as SKS to make them into a theme, then save it as either .theme, .desktopx, .desktop, .wb etc! and then upload it to here using an account specifically for you!
Hope this helps along with everyone elses contribution!