Background Change Problem

Hello,

I have designed my opening page on the style of frames
but using CSS. So, in other words I have 4 different
classes in the body element,each having its own
background image.
after calling these classes in the body of the html
code, on the remaining poriton of the body I have
added an image button. (img src)
What I am trying to achieve is that, I want the
background Image of each of the 4 classes to change
when the mouse moves over the image button.

I have been unable to get this.

Could anyone please help me with this problem?

Thanks,Mala

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