In older versions of Outlook you can shrink the header down to the subject line by editing the view or by carefully right clicking on the left edge of the reading pane and selecting Header Information to toggle it off and on.
In Outlook 2007, only the subject shows (as seen in the screenshot below); while in Outlook 2003, the entire header disappears and you only see the message body in the reading pane.
Hiding the header is not supported in Outlook 2010. Yes, View's Other Settings options includes the option to hide the message header, but enabling it does nothing. Microsoft removed this capability and forgot to remove it from the view settings when they disabled the feature.
Published Jan 2 2012