I've just started programming in Rails, so my comment may not count for much, but it seems to me that you're trying to put a method in the layout, and layouts, as far as I know, accepts built-in helper methods. Because it's not correlated with the folder named off of the controller you're using, the layout can't find the variable @rposts; layouts doesn't receive any data from the controller branching off of Application Controller.
I'd advise you to create a partial instead. Partials are rhtml files whose name starts with an underscore (for example: '_post.rhtml'). Put that into the controller file, and then bring that up in the layout via the code line: <%=render(:partial=>"post")%>
