hi
open Siscontents, go to: file -> new package -> s60 theme package.
Now open your ROFS1 with nokia cooker and select the files in siscontents.
(resource\skins\101f84b9 and Private\10207114\import\101f84b9\series60skin.skn)
You don't need the .dll, it works without.
Than click on contents, double click on the .skn.
Here you can modify it.
After you finished save it as .sis, open the .sis with siscontents and extract it to ROFS1. If you get asked overwrite the files.
Save ROFS1 and flash.