Change table background image On CLICK

I am designing a PHP page in dreamweaver CS5.  I have a tabe with a background image. 

Is there a simple code that will allow me to change the image preferably on a hover or a click. Ideally I want to get the image from the database using echo function.  I have called the table ID "td1".

Table code is:

<table width="89%" border="0" cellpadding="0" cellspacing="2" style="background:url(graphics/colourboxcream.png) no-repeat" id="td1">

Please, please, help 

Sounds like a javascript.

This came up on a google search: http://www.webdeveloper.com/forum/showthread.php?t=173149

If you dont need the image to remain the same, then use css :hover or :active

easy to say and I am using CSS but I cant work out what the code is to change the background.  Not sure how to define the table.  Is it a get element ID or a table.id.background-image or some other code to point to the actual table?  Sorry for being a div but I know how to change the image and how to use CSS but I am having trouble trying to work out the the actual function that will change the property when clicked or hovered?

document.getElementById('id').style.backgroundImage="url('img.png')";

Should do it.