Yea that's possible css alright.
I think I know what you're wanting to achieve.
Basically, use the hover to enable the link that's being clicked on to change the colour of the background. Use a class to show the current link that's active.
I found a solution to something similar a while ago on http://www.htmldog.com/articles/suckerfish/dropdowns/
I've implemented it on http://www.wallswelldrilling.ie/index2.htm, feel free to look around the code. It'll do exactly what you want using css, in xhtml, it's accessible too and validates.
I have created a vertical menu with a white background, once a link is clicked i want that menu item's background color to change. Then once another menu item is clicked the first menu items background goes back to white and the new item's background color changes. I guess i want something similar to gmail's navigation. I am just wondering if that is possible in CSS, and maybe some code or help on how to tackle this. Thanks in advance for any information.