There are two reasons e-mail messages look incorrect when viewed in Outlook 2007. The first reason is related to the new method Outlook 2007 uses to display the message. E-mail messages are generally formatted using HTML. HTML is the same language used to create web pages. In previous versions of Outlook e-mail messages were displayed using the same methods employed by Internet Explorer. Outlook 2007 changed this and now uses the methods employed in Microsoft Word. Word does not have the same level of support for HTML that Internet Explorer does. For a list of the support HTML tags in Outlook 2007 look here:
The second reason Outlook 2007 may cause an e-mail's formatting to appear incorrect is the "DPI" setting. This setting is located in your display settings in the Windows Control Panel. The DPI setting must be on the default setting of "96 DPI" to ensure Outlook 2007 displays the message correctly.