Are you trying to do it so it will be XHTML/CSS compliant, because you are going to want to use CSS - not fireworks - definitely. If you use the CSS hover effect you can accomplish the same effect as Fireworks and Dreamweaver without having accessibility issues - look here:
Here is the example:
http://www.tutorio.com/media/css-tut...er-example.htm
Here is the tut:
http://www.tutorio.com/tutorial/pure...mage-rollovers
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Greg