Select "Display as HTML" to enable HTML for the selected email. Click the InfoBar again if the message contains images that are not displaying. Click "Download Pictures" to display them.

PowerPoint 2007 saves presentations as Web pages, converting files to HTML with a single step. PowerPoint 2010 disabled this function, but it saves presentations as images which you can embed ...

In order to embed HTML, you actually need to copy the rendered HTML from either an existing web page or WYSIWYG HTML editor and then paste it into Gmail.