Viewing Microsoft Entourage email messages in the Finder with Quick Look doesn't work -- it merely displays an icon image. If you have Entourage 2008 and 10.5 or 10.6, there is a way to display the contents of the message in Quick Look. Download the file named Entourage QuickLook Plug-In.dmg from this site, and place a copy in the /Library/QuickLook folder.
This solution is especially useful for scrolling through Spotlight search results in the Finder, with Quick Look opened in full screen mode on a second monitor.
[robg adds: The plug-in should also work in your user's Library/QuickLook folder. I don't use Entourage, though, so I can't test this one.]
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http://hints.macworld.com/article.php?story=20091027123517914