WP Nav Menu Seperator

I would like to have a horizontal navigation bar all one rectangular piece with a 1px image set to repeat across it and also a hover which will also just be like a 1px bar repeated across the hovered tab. I need a graphic seperator though for each of the tabs like a | but a 2px custom image I have heard of list:after or list:before in the functions.php? Not quite sure how to really get it set up though. Any help please.