correct placement of custom header image fails

sorry guys, i don't get it. i want to put a custom header image in my theme, but i'm not a webdesigner and i don't get it to work. i use css and i deal a bit with php-templates, but i'm not professional in both scenarios.

my problems: placing the header image (960px, 90px) in the page.tpl.php (via img src) template with several z-index, position and other paramaters doesn't show the image correctly.

so i switched to use a block with an own css class header image, and the result is like in the attached image. changing z-index from -100 to whatever doesn't help, position doesn't work: i can't get the image in the background with the logo and the searchbox on it. at least the bottom of the image must be shown 4px lower behind the navbar (overlapping).

the image header module doesn't help me and i don't need it.

what am i doing wrong? i don't see a special point for that in the m_a_m documentation and i don't see a hook in the style/theme/template of mix and match and/or fusion for the header. probably i don't know enough here.

i would appreciate every help or hint or link to deeper documentation.

thanks in advance and greets,

karsten