php Expanding Menu System Wanted

Hi there I want to create a very basic menu system in php that I can include on all pages of my site and by changing one external file be able to change the navigation on all pages. The navigation will only have two levels. There should be an easy way for the navigation to know what page it is on and be expanded to the relevant section (ie every page has a unique name in it that the menu retrieves??). The navigation will use images and I want it to be able to highlight (image swap) the current page in the navigation. Every click will take a user somwhere...ie in the nav below if I click nav item two it will take me to that page and the sub nav of this section will be open. nav item one subnav1 *subnav2* subnav3 nav item two nav item three I do not need or want to use frames if you need to know that. I am sure there are probably lots of these menu systems out there but as I do not reall y know where to look your input would be very grateful....thanks in advance...James