It depends on what the 'content' is. If it's just text, then you can simply put a TMemo on the right hand side, and clear that and rewrite it each time you need to display different text.
But if you're talking about a more complex display which has several different layouts, then one way would be to be to put several TPanels on top of one another at the right hand side and set up each one to have the layout you want for one of the menu items. Then you could use Panelx.BringToFront to display the appropriate panel.
Eric