You can make any image change onmouseover.
HTML Code:
<img src="some.jpg" onmouseover="this.src='someother.jpg';" onmouseout="this.src='some.jpg';">
But to do that with an image map, well it depends upon just what sort of effect you are going for. You could probably overlay a section of a map with a different image. You also should be able to set map coords outside of the main image and have other smaller images in those locations that could roll over.
As an alternative to an image map - doesn't image ready also allow for slices? If so, these could be rollovers as well as links.
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