There is an article on the site, dating back to 2007 "Do image maps work in HTML emails?" which i found whilst trying to fix a similar problem that Nick Poulos (last post) had.
To summarise he found that in preview... or as a webpage his images were fine, in both position and dimensions. However, when he viewed his email in outlook the image map, was position incorrectly, it was higher than anticipated.
I have had a similar problem, and despite a quick search I haven't found an answer in the forum to his problem.
However I have after some experimentation found the problem. It seems to go wrong when there is padding or margin on the image, after declaring margin: 0; and padding 0; it seems to work.
Not sure on this... i also have a feeling it has something to do with editing the image with image maps already associated with the image... i.e if you have an image that is 400px high then change it to say 350px, i think the image maps don't always translate correctly