Theme is created with Macromedia Fireworks MX, but almost noone has it so
i exported logo background to bmp file that can be used with any editor.

After you create logo it should be splitted in 2 images:
logo1.gif and logo2.gif

width of logo1.gif should be the same as width of logo2.gif
height of logo1.gif is 23px
height of logo2.gif is 30px

if width of image will be different from "130" then open overall_header.tpl
with notepad (or any other text editor) and replace all "130" width width of
your logo.

html code for header is in overall_header.tpl file (tpl files are usual html files)