Mouse over effect on target

I have a client that wants a part of the main page (typically where a slider pane would be) to show an image when a user mouse overs a button that is underneath this pane.

The problem is, they don’t just want it to be a larger image of the button, they want a different image altogether… so when you hover over the ‘Donate’ button, the pane will show a certain .jpg

Can anyone possibly help me with this? I can’t find any answers as it’s a hard question to ask!