adding a separator to categories

im using wordpress 2.8.6

Im not a programmer but i want to modify a menu to show an image as separator for categories instead of a white line if possible

this is wht i think is the code block making the menu

<?php
$cats = get_option(‘uwc_category_include’);
if($cats) {
if(strtolower($cats) == “all”) {
wp_list_categories(‘title_li=’);
} else {
wp_list_categories(‘title_li=&include=’.$cats);
}
} else {
wp_list_categories(‘title_li=&number=8’);
}
?>

ive been searching and reading wordpress documentation but i think it is over my level of knowledge

and would you please recommend me wht to read in the future to be more educated on understanding these pieces of code in wordpress installation, should i read php tutorials, or a begginer wordpress coding tutorial somewhere, would you leave a link to something on the like doing ppl like me understand this blocks better at least for little customizations.