header generation problem

I'm trying to create a single dynamic header for a wide range of web pages which I'll just include as I need it. There are a few things that change per web page in the header, but I've settled all the issues except a good way of how to modify a single image that changes based on the web page being displayed. For example: I'm displaying index.php, which includes 'header.php', the variable $wpid indicates that the current web page is index.php. Now index.php needs to display: (changing index_off.gif to index_on.gif) index_on.gif anotherpage_off.gif yetanotherpage_off.gif (the tricky part is that each image will change to on depending on what page is being displayed) I really haven't come up with an adequate solution. Ideas? Thanks. Jon