Creating a customized skin for galleru 1.5.10

The following information is required to get an answer:
Get this information from the PHP diagnostic (in the configuration wizard).
Gallery URL (optional but very useful):
Gallery version:1.5.10
Apache version:Apache-AdvancedExtranetServer/2.0.50
PHP version (don't just say PHP 4, please): PHP/4.3.8
Graphics Toolkit:
Operating systemMandrakelinux/7mdk)
Web browser/version (if applicable):

Dear,

I am creating a gallery for our Ju-Jutsu Club.
I would like to create a skin with the logo of our club as watermark and as image ( like the butterfly in the butterfly skin). Can anybody tell me how to do this ? Can anyone help me out ?

Thanks a lot,

Yours Sincerely,

Peter