Ported the solution to SP2010. Read the details her:
http://sharepointjavascript.wordpress.com/2011/09/12/preview-metadata-in-list-view-on-mouseover-updated-version

v1.0.0		15.09.2011: Bugfix as it did not work in a Document library.
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v1.1		Added some new features, see this article for details:
		http://sharepointjavascript.wordpress.com/2011/09/12/preview-metadata-in-list-view-on-mouseover-updated-version