Web Forms :: Change Image Source On Master Page?

I have a web site with a navigation bar on the left side that uses image buttons to select the page you want to see. Each button has 3 possible images - the normal image when the page is not selected, the mouseover image when the the mouse is over the button, and the selected image when the button has been clicked and the page selected. Formerly each web page had its own navigation bar but I have moved the common content into a master page.

The problem I have is how to make the button image of the selected page to be the "selected" image rather than the "normal" image. Basically I need to change the imagebutton source to the "selected" image when a button is clicked and reset it to the normal image when a different button is clicked.

Currently the Javascript looks like this:

var loaded = new Array();
function F_loadRollover(image,imageName) {
if (image && image.src &&
(null == image.out || typeof(image.out) == typeof(void(0)))) {
s = image.src;

[Code]....

How can I tweak the Javascript so that the src of the clicked image is "content1_selected" instead of "content1_normal" and then reset it when another button is clicked. This seems like it would be a common need when moving a navigation bar to a master page to eliminate redundant code.